how could I know the contractions

can any one tell me how contraction work


At home when he's finished eating, he goes into the kitchen and washes up his plates.


in this sentence the contraction is he has

but most of the time my guess will be wrong. Is there any lessons in Usingenglish.com for contraction? Please help me.Due to these kind of confusion I cannot understand a novel in English completely.

When in doubt, look for the past participle form. The rule is has + past participle.

Ex: He's red, not green. = He is red.
Ex: He's read the book. = He has read the book.

Verb 'to read'
present: read
past: read
past participle: read (pronounced like the color 'red')

Contractions-anglais

hello I send you this link which can help you !
:-)