A little peculiarity of those words who have the sound  in the stem and say farewell to it in the plural: Masculine Neuter Sing. Pl. Sing. Pl.N dg (day) dagas ft (vessel) fatuG dges daga ftes fataD dge dagum fte fatumA dg dagas ft fatu
Examples of a-stems: earm (an arm), eorl, helm (a helmet), hring (a ring), m (a mouth); neuter ones - dor (a gate), hof (a courtyard), geoc (a yoke), word, dor (an animal), bearn (a child), gar (a year).
ja-stems Singular Masculine NeuterN hrycg (back) here (army) ende (end) cynn (kind) rce (realm)G hrycges heriges endes cynnes rcesD hrycge herige ende cynne rce A hrycg here ende cynn rce PluralN hrycgeas herigeas endas cynn rciuG hrycgea herigea enda cynna rcea D hrycgium herigum endum cynnum rciumA hrycgeas herigeas endas cynn rciu
Again the descendant of Indo-European jo-stem type, known only in masculine and neuter. In fact it is a subbranch of o-stems, complicated by the i before the ending: like Latin lupus and filius. Examples of this type: masculine - wecg (a wedge), bcere (a scholar), fiscere (a fisher); neuter - net, bed, wte (a punishment).
wa-stems Singular Plural Masc. Neut. Masc. Neut.N bearu (wood) bealu (evil) bearwas bealu (-o)G bearwes bealwes bearwa bealwaD bearwe bealwe bearwum bealwumA bearu (-o) bealu (-o) bearwas bealu (-o)
Just to mention. This is one more peculiarity of good old a-stems with the touch of w in declension. Interesting that the majority of this kind of stems make abstract nouns. Examples: masculine - snw (snow), aw (a custom); neuter - searu (armour), trow (a tree), cnw (a knee)
-stems Sg.N swau (trace) fr (journey) tigol (brick)G swae fre tigoleD swae fre tigoleA swae fre tigole Pl.N swaa fra tigolaG swaa fra tigolaD swaum frum tigolumA swaa fra tigola
Another major group of Old English nouns consists only of feminine nouns. Funny but in Indo-European they are called a-stems. But Germanic turned vowels sometimes upside down, and this long a became long o. However, practically no word of this type ends in -o, which was lost or transformed. The special variants of -stems are jo- and wo-stems which have practically the same declension but with the corresponding sounds between the root and the ending.
Examples of -stems: caru (care), sceamu (shame), onswaru (worry), lufu (love), lr (an instruction), sorg (sorrow), rg (a season), ides (a woman).Examples of j-stems: sibb (peace), ecg (a blade), secg (a sword), hild (a fight), x (an axe).Examples of w-stems: beadu (a battle), nearu (need), ls (a beam).
i-stems Masc. Neut. Sg.N sige (victory) hyll (hill) sife (sieve)G siges hylles sifesD sige hylle sifeA sige hyll sife Pl.N sigeas hyllas sifuG sigea hylla sifaD sigum hyllum sifumA sigeas hyllas sifu
The tribes and nations were usually of this very type, and were used always in plural: Engle (the Angles), Seaxe (the Saxons), Mierce (the Mercians), Norymbre (the Northumbrians), Dene (the Danish)
N DeneG Dena (Miercna, Seaxna)D DenumA Dene
Fem. Sg. Pl.N hyd (hide) hde, hdaG hde hdaD hde hdumA hd hde, hda
This kind of stems included all three genders and derived from the same type of Indo-European stems, frequent also in other branches and languages of the family.
Examples: masculine - mere (a sea), mete (food), dl (a part), giest (a guest), drync (a drink); neuter - spere (a spear); feminine - cwn (a woman), wiht (a thing).
u-stems Masc. Fem. Sg.N sunu (son)feld (field) duru (door) hand (hand) G suna felda dura handaD suna felda dura handaA sunu feld duru hand Pl.N suna felda dura handaG suna felda dura handaD sunum feldum durum handumA suna felda dura handa
They can be either masculine or feminine. Here it is seen clearly how Old English lost its final -s in endings: Gothic had sunus and handus, while Old English has already sunu and hand respectively. Interesting that dropping final consonants is also a general trend of almost all Indo-European languages. Ancient tongues still keep them everywhere - Greek, Latin, Gothic, Old Prussian, Sanskrit, Old Irish; but later, no matter where a language is situated and what processes it undergoes, final consonants (namely -s, -t, often -m, -n) disappear, remaining nowadays only in the two Baltic languages and in New Greek.
Examples: masculine - wudu (wood), medu (honey), weald (forest), sumor (a summer); fem. - nosu (a nose), flr (a floor).
The other type of nouns according to their declension was the group of Weak nouns, derived from n-nouns is Common Germanic. Their declension is simple and stable, having special endings:
Masc. Fem. Neut. Sg.N nama (name) cwene (woman) age (eye)G naman cwenan aganD naman cwenan aganA naman cwenan age Pl.N naman cwenan aganG namena cwenena agenaD namum cwenum agumA naman cwenan agan
Examples: masc. - guma (a man), wita (a wizard), steorra (a star), mna (the Moon), dma (a judge); fem. - eore (Earth), heorte (a heart), sunne (Sun); neut. - are (an ear).
And now the last one which is interesting due to its special Germanic structure. I am speaking about the root-stems which according to Germanic laws of Ablaut, change the root vowel during the declension. In Modern English such words still exist, and we all know them: goose - geese, tooth - teeth, foot - feet, mouse - mice etc. At school they were a nightmare for me, now they are an Old English grammar. Besides, in Old English time they were far more numerous in the language.
Masc. Fem. Sg.N mann ft (foot) t (tooth) | hnutu (nut) bc (book) gs (goose) ms (mouse) burg (burg)G mannes ftes tes | hnute bce gse mse burgeD menn ft t | hnyte bc gs ms byrigA mann ft t | hnutu bk gs ms burg Pl.N menn ft t | hnyte bc gs ms byrigG manna fta ta | hnuta bca gsa msa burgaD mannum ftum tum | hnutum bcum gsum msum burgumA menn ft t | hnyte bc gs ms byrig
The general rule is the so-called i-mutation, which changes the vowel. The conversion table looks as follows and never fails - it is universally right both for verbs and nouns. The table of i-mutation changes remains above.Examples: fem. - wfman (a woman), c (an oak), gt (a goat), brc (breeches), wlh (seam), dung (a dungeon), furh (a furrow), sulh (a plough), grut (gruel), ls (a louse), rul (a basket), a (water), niht (a night), m'g (a girl), scrd (clothes).
There are still some other types of declension, but not too important fro understanding the general image. For example, r-stems denoted the family relatives (dohtor 'a daughter', mdor 'a mother' and several others), es-stems usually meant children and cubs (cild 'a child', cealf 'a calf'). The most intriguing question that arises from the picture of the Old English declension is "How to define which words is which kind of stems?". I am sure you are always thinking of this question, the same as I thought myself when first studying Old English. The answer is "I don't know"; because of the loss of many endings all genders, all stems and therefore all nouns mixed in the language, and one has just to learn how to decline this or that word. This mixture was the decisive step of the following transfer of English to the analytic language - when endings are not used, people forget genders and cases. In any solid dictionary you will be given a noun with its gender and kind of stem. But in general, the declension is similar for all stems. One of the most stable differences of masculine and feminine is the -es (masc.) or -e in genitive singular of the Strong declension.
Now I am giving another table, the general declension system of Old English nouns. Here '-' means a zero ending.
Strong declension (a, ja, wa, у, jу, wу, i -stems).