Since and for are both used for situations and actions that start in the past and continue to the present. For example:
- I've been at home for 4 hours.
- I've been at home since 12.00.

Since is used wiuth a point of time. For example:
- I've lived here since March.
- I've been here since 9.00 this morning.

Since is only used with perfect forms such as the Present Perfect, Past Perfect and so on - it cannot be used with other forms. For example:
- I've studied english since last year - Correct
- I studied / I am studying / I will study English since last year - Incorrect

Since is also used with time clauses. For example:
- I've studied English since I was at universiity.
- We haven't seen my family since we got married.
Note that the main clause uses the Present Perfect, wheras the other clause uses the Past Simple.

For is used with a period of time. For example:
- I've lived here for 9 months.
- She's been here for 5 hours.

Unlike since, for can be used with tenses other than perfect tenses. For example:
- I lived here for 9 months - This period of time started and ended in the past, it is now finished.
- I will live here for a year - This period of time will start and end in the future, it hasn't started yet.
- I have lived here for a long time - This period of time started in the past and continues to the present. It isn't finished yet.

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