Infinitive, Past singular, Past plural, Participle II (or Past Participle) Class Iwrtan (to write), wrt, writon, writensnpan (to cut), sn, snidon, sniden Other examples: belfan (stay), clfan (cling), ygrpan (clutch), btan (bite), sltan (slit), besmtan (dirty), gewtan (go), blcan (glitter), scan (sigh), stgan (mount), scnan (shine), rsan (arise), lan (go).
Class IIbodan (to offer), bad, budon, bodencosan (to choose), cas, curon, coren Other examples: cropan (creep), clofan (cleave), flotan (fleet), gotan (pour), grotan (weep), notan (enjoy), scotan (shoot), logan (lie), browan (brew), drosan (fall), frosan (freeze), forlosan (lose).
Class III III a) a nasal consonantdrincan (to drink), dranc, druncon, druncen Other: swindan (vanish), onginnan (begin), sinnan (reflect), winnan (work), gelimpan (happen), swimman (swim). III b) l + a consonanthelpan (to help), healp, hulpon, holpen Other: delfan (delve), swelgan (swallow), sweltan (die), bellan (bark), melcan (milk). III c) r, h + a consonantsteorfan (to die), stearf, sturfon, storfenweoran (to become), wear, wurdon, wordenfeohtan (to fight), feaht, fuhton, fohten More: ceorfan (carve), hweorfan (turn), weorpan (throw), beorgan (conceal), beorcan (bark).
Class IVstelan (to steal), st'l, st'lon, stolenberan (to bear), b'r, b'ron, boren More: cwelan (die), helan (conceal), teran (tear), brecan (break).
Class Vtredan (to tread), tr'd, tr'don, tredencwean (to say), cw', cw'don, cweden More: metan (measure), swefan (sleep), wefan (weave), sprecan (to speak), wrecan (persecute), lesan (gather), etan (eat), wesan (be).
Class VIfaran (to go), fr, fron, faren More: galan (sing), grafan (dig), hladan (lade), wadan (walk), dragan (drag), gnagan (gnaw), bacan (bake), scacan (shake), wascan (wash).
Class VIIhtan (to call), ht, hton, htenfeallan (to fall), feoll, feollon, feallencnawan (to know), cnow, cnowon, cnwen More: blondan (blend), ondr'dan (fear), lcan (jump), scadan (divide), fealdan (fold), healdan (hold), sponnan (span), batan (beat), blwan (flourish), hlwan (low), spwan (flourish), mwan (mow), swan (sow), rwan (turn).
So the rule from the table above is observed carefully. The VII class was made especially for those verbs which did not fit into any of the six classes. In fact the verbs of the VII class are irregular and cannot be explained by a certain exact rule, though they are quite numerous in the language.
Examining verbs of Old English comparing to those of Modern English it is easy to catch the point of transformation. Not only the ending -an in the infinitive has dropped, but the stems were subject to many changes some of which are not hard to find. For example, the long in the stem gives i with an open syllable in the modern language (wrtan > write, scnan > shine). The same can be said about a, which nowadays is a in open syllables pronounced  (hladan > lade). The initial combination sc turns to sh; the open e was transformed into ea practically everywhere (sprecan > speak, tredan > tread, etc.). Such laws of transformation which you can gather into a small table help to recreate the Old word from a Modern English one in case you do not have a dictionary in hand, and therefore are important for reconstruction of the languages.
Weak verbs in Old English (today's English regular verbs) were conjugated in a simpler way than the strong ones, and did not use the ablaut interchanges of the vowel stems. Weak verbs are divided into three classes which had only slight differences though. They did have the three forms - the infinitive, the past tense, the participle II. Here is the table.
Class I Regular verbs Inf. Past PPdman (to judge), dmde, dmedheran (to hear), herde, herednerian (to save), nerede, neredstyrian (to stir), styrede, styredfremman (to commit), fremede, fremedcnyssan (to push), cnysede, cnysed
When the suffix is preceded by a voiceless consonant the ending changes a little bit:cpan (to keep), cpte, cpt / cpedgrtan (to greet), grtte, grt / grted
If the verb stem ends in consonant plus d or t: sendan (to send), sende, send / sendedrestan (to rest), reste, rest / rested
Irregularsellan (to give), sealde, sealdtellan (to tell), tealde, tealdcwellan (to kill), cwealde, cwealdt'can (to teach), thte, thtr'can (to reach), rhte, rhtbycgan (to buy), bohte, bohtscan (to seek), shte, shtwyrcan (to work), worhte, worhtencan (to think), hte, htbringan (to bring), brhte, brht
Other examples of the I class weak verbs just for your interest: berian (beat), derian (harm), erian (plough), ferian (go), herian (praise), gremman (be angry), wennan (accustom), clynnan (sound), dynnan (resound), hlynnan (roar), hrissan (tremble), scean (harm), wecgean (move), fran (go), l'ran (teach), drfan (drive), fsan (hurry), drgean (dry), hepan (heap), mtan (to meet), wscean (wish), byldan (build), wendan (turn), efstan (hurry). All these are regular.
Class IImacian (to make), macode, macodlufian (to love), lufode, lufodhopian (to hope), hopode, hopod
Tis class makes quite a small group of verbs, all of them having -o- before the past endings. Other samples: lofian (praise), stician (pierce), eardian (dwell), scawian (look), weorian (honour), wundrian (wonder), fstnian (fasten), mrsian (glorify).
Class IIIhabban (to have), hfde, hfdlibban (to live), lifde, lifdsecgan (to say), sgde, sgdhycgan (to think), hogde, hogodragan (to threaten), rade, radsmagan (to think), smade, smadfrogan (to free), frode, frodfogan (to hate), fode, fod
Old English verbs are conjugated having two tenses - the Present tense and the Past tense, and three moods - indicative, subjunctive, and imperative. Of these, only the subjunctive mood has disappeared in the English language, acquiring an analytic construction instead of inflections; and the imperative mood has coincided with the infinitive form (to write - write!). In the Old English period they all looked different.
The common table of the verb conjugation is given below. Here you should notice that the Present tense has the conjugation for all three moods, while the Past tense - for only two moods (no imperative in the Past tense, naturally). Some more explanation should be given about the stem types.
In fact all verbal forms were generated in Old English from three verb stems, and each verb had its own three ones: the Infinitive stem, the Past Singular stem, the Past Plural stem. For the verb wrtan, for example, those three stems are: wrt- (infinitive without the ending -an), wrt- (the Past singular), writ- (the Past plural without the ending -on). The table below explains where to use this or that stem.