USING SINCE AND FOR

Example using SINCE

I have been here since eight o’clock.
I have been here since Tuesday.
I have been here since May.
I have been here since 1999.
I have been here since January 3, 2001.
I have been here since yesterday.
I have been here since last month

Since is followed by the mention of a specific point in time: an hour, a day, a month, a year, etc. Since expresses the idea that something began at a specific time in the past and continues to the present.

CORRECT: I have lived here since May.
CORRECT: I have been here since May.

INCORRECT: I am living here since May.
INCORRECT: I live here since May.
INCORRECT: I lived here since May.
INCORRECT: I was here since May.

Example using FOR

I have been here for ten minutes.
I have been here for two hours.
I have been here for five days.
I have been here for about three weeks.
I have been here for almost six months.
I have been here for many years.
I have been here for a long time.

For is followed by the mention of a length of time: two minutes, three hours, faur days, five weeks, etc. Note: if the noun ends in -s (hours, days, weeks etc.), use for in the time expression, not since.

a. I have lived here for two years. I moved here two years ago, and I still live here.
b. I lived in Athens for two years. I don’t live in Athens now.

In (a): The use of the present perfect in a sentence with for + a length of time means that the action began in the past and continues to the present.
In (b): The use of the simple past means that the action began and ended in the past.