The English language was cobbled together from many and varied source languages, by virtue of the settlers and conquerors of the British Isles at around the formation time of the English language. Consequently there are many grammar rules which do not apply to all parts of the language because of the different origins of certain words. There are therefore regular and irregular forms.
A ‘regular verb’ forms its past and past oarticiple by adding –ed or –d to the base form. E.g. BASE FORM laugh, talk, like. PAST FORM laughed, talked, liked. PAST PARTICIPLE laughed, talked, liked.
Some regular verbs undergo spelling changes when a suffix that begins with as vowel is added. E.g. fry + ed = fried, stop + ed = stopped.
An ‘irregular verb’ forms its past and past participle in some way other than by adding –ed or –d to the base form.
E.g. BASE FORM (be, am, are, is), bear. beat, become. PAST FORM (was, were), bore, beat, became. PAST PARTICIPLE been, borne, beaten or beat, become.
There is no rule for remembering the irregular forms and it will mostly be a matter of learning and memorizing the spelling of each form. For instance, ‘seek’ becomes ‘sought’ but ‘leak’ becomes ‘leaked’ not ‘lought’. Lists of irregular verb forms can be easily found in book stores and online.
Some verbs in English can have two different past forms. The word ‘dream’ can be rendered as an irregular form ‘dreamt’ in the past tense, or the regular form ‘dreamed’. ‘Dreamt’ is mostly used in British English while ‘Dreamed’ is usually the American usage.