when we use since and for

we often use 'for' and 'since' with the present perfect tense.

• we use 'for' to talk about a period of time-5 minutes,2 weeks ,6 years.
• we use 'since' to talk about a piont in a past time-9o'clock,1st january ,monday.

for examples:

1. i have been here for 20 minutes.
2. i have been here since 9 o'clock.
3. john has not called for 6 months
4. john has not called since february.