Rules of tenses.. perfect tense imp
Sub+helping verb ( has,have) + third form of verb + object
"Has" used with singular subject.
"HAVE" used with plural subject except I & YOU.
I have just bought a pen.
She has written a letter.
SUB+ HELPING VERB ( had) + third form of verb + object
Eg. He had finished his work.
Future perfect tense
Sub+ helping verbs (shall/will+ have ) + third form of verb + object
I shall have finished my work.