The prepositions for and since are often used with the present perfectThe aspect expressing completion. E.g.: He’s finished university. tenseA grammatical category that is marked by verb inflection. To express when an event or action happens in time or when a state exists, we use tenses.. For is used with an incomplete period of timeA period of time that includes the time of speaking. E.g.: I have known him for two years. ("for two years"), while since with a point of timeA particular moment in time. E.g.: She came home at six. ("six") I was born in 1980. ("1980") .

I have lived here for two months. (period)
I have lived here since January. (point of time)

For questions we use How long...? and Since when...? :

"How long have you lived here?"
"For ten years." (or "Since 2002.")

"Since when have you lived here?"
"(Since) 2002."

The point of time after since can also be expressed with a time clauseA group of related words containing a subject and a verb., in which the past simple is used.

I have lived here since I was born.

Diagrams

Present perfect with JUST
Present perfect IT'S + period + SINCE