The use of SINCE
The word since represents the word "from." It is used to convey a relationship of a phenomenon which happened from a particular time point.
Since is an adverb meaning "from then until now".
Ex: She was appointed in May and has been supervisor ever since.
It is also used as an adverb meaning "between a particular past time and the present, subsequently".
Ex: They had at first refused to cooperate, but have since agreed to volunteer
As a preposition, since means "continuously from".
Ex: It has been rainy since June.
It is also used as a preposition meaning "between a past time or event and the present".
Ex: There have been many changes since the merger.
As a conjunction, since means "in the period following the time when".
Ex: He has called since he changed jobs.
Since is also used as a synonym for "because".
Ex: Since you're here early, let's begin.
The use of FOR
For is used when we measure the duration – when we say how long something last.To measure a period of time up to the present, we use the present perfect tense and not the present tense.
Examples of Since:
Since you're losing weight, make sure you drink plenty of water!
Since it's so hot, I'll have an iced coffee.
I can't take him with me since he's ill.
From then until now or between then and now: They left town and haven't been here since.
Continuously from: They have been friends since childhood.
Intermittently from: She's been skiing since childhood.
Its been a long time since we have spent time together.
Examples of For:
They exercise for two hours every day.
They are exercising for three hours today.
He has lived in Moscow for a long time.
He has been living in Turin for three months.
I worked at the service station for five years.
He will be in hospital for at least a week.