for + a period of time and since + a point in time are two ways of saying the same thing.
for a few days / for five years / for ages
since Saturday / since I left school / since 1999
been is the past participle of go as well as be.
He hasn’t been to the doctor yet. (go)
Have you been abroad this year? (go)
Note: gone is also a past participle of go.
gone = go and not come back.
been = go and come back.
Present Perfect Simple and Continuous
You can use the present perfect when you want to say how long something has continued from a point in the past up to now. For verbs with stative meanings you always use the simple form.
I’ve been a student for two years.
She’s known Tommy since they were at school.
For verbs with dynamic meanings you usually use the continuous form.
My friend’s been playing tennis since she was eight.
Note: You can use the simple form for very unchanging, ‘permanent’ situations. Compare:
I’ve been living here since July. ( Temporary)
I‘ve lived here all my life. (Permanent)
Just another quick look at English grammar. Read through it, think about it, and use it.
Good luck with your English language learning.