For, Since and During
For: Used to express a quantity of time, or the duration of something.
"I have been living here for 8 months"
"I am going to stay here for 1 year"
"How long will you go there for?"
Since : Used to express when something started. Relates to a specific time in the past.
"I have been living here since October"
"Since we met, I have not stopped thinking about you"
"I have know him since I was very young"
During: Used with nouns in order to say what happens inside a period of time.
"During my time here, I have visited a lot of beautiful places."
"I hate when people talk a lot during films."
"I love going to the beach during summer"