Since - For

Since

• used to show the starting of a point
• action will be going on at the moment of speaking

Ex:

• We haven't seen him since his birthday.
• We haven't played soccer since May.

General Structures:

• 1990
• May
• last year
• Christmas
• yesterday
• my wedding day
• she left you
• yesterday
• then
• I was born

For

• to show a period of time
• here too the action will be continuing

Ex:

• Ken has studied English for two months.
• Barnie hasn't come to school for two days.

General Structures:

• a day
• ten months
• three weeks
• six years
• two hours
• a long time
• several hours [GrammarBank](SINCE vs FOR - GrammarBank)