When is the present perfect tense used instead of the past tense?
I know that the present perfect tense is used when some adverbs (e.g., never, ever) are present in the sentence; the same is true for sentences like the following one.
When you returned, I have been at home since 3:00 PM.
In which other cases should I use the present perfect? Do the following sentences require it?
I have walked downtown everyday for a year.
I have been at home since 3:00 PM.