For or Since
"For" and "since" are prepositions used to talk about time.
This is used to refer to an amount or a period of time - "for" is always before the period of time.
"She disappeared for 3 days."
"I haven't seen you for ages."
"For" cannot be used with "all"
Time expressions with "all" cannot be used with "for." These are expressions like "all day," "all week," or "all my life."
"We were packing all day."
Not - "We were packing for all day."
"For" with different tenses
"For" can be used with a variety of different tenses, because time periods can occur in the past, present and future.
"I lived in Malaysia for a year."
"I'm travelling for two weeks."
"I'll be in Seoul for 9 days."
Exception - Present simple tense
The tricky one is the present simple tense. You can use it when stating a fact or making a general statement.
"A sunset typically lasts for about five minutes."
"Some wait for as long as two years to get a visa."
However, if you want to talk about continual occurrences, present simple can't be used with "for."
"I live in Australia."
Not - "I live in Australia for 15 years."
"Since" is used to refer to the starting point of a period of time. It always comes before the time or an event.
"She's been gone since 12.30."
"We haven't talked since last week."
"I haven't seen you since Jane's birthday."
"Since" with perfect tenses
Because "since" only refers to the starting point of a time period in the past, it can only be used with perfect tenses.
Past perfect continuous:
"I had been waiting since 5 o'clock."
"I've known him since we were kids."