The first thing you should do is read an explanation in a grammar or course book; then do the associated exercises; and then write your own sentences. You could then post your sentences and specific queries here and we can help you usefully.

-We use THE PRESENT PERFECT for actions which started in the past and are still happening now. ex; I've known Julie for ten years (and I still know her). Structure: Affirmative: Subject + Have / Has + Past Participle Negative: Subject + Haven't / Hasn't + Past Participle Question: Have / Has + Subject + Past Participle AND We use the past simple for past events or actions which have no connection to the present.. ex; I knew Julie for ten years (but then she moved away and we lost touch). Structure: Affirmative; subject + verb (in past form) + complement. Negative; subject + auxiliary verb (did) + negacion + verb (infinitive) + complement Interrogative; auxiliary verb (did) + subject + verb (infinitive) + complement?.

The Past Simple tense in English is used with actions that are completed and do not affect the present. For example, "I walked the dog." The Present Perfect tense, however, is used with actions that occurred in the past yet continue to affect the present in some way. For example, "I have eaten today," "I have known her for ten years."