Since and For are easily confused words, with one word often being used in place of the other. However, there is definitely a difference between since and for. If you understand the meanings of since and for, you will know the correct usage of both the words.
Since is an adverb as well as a conjunction.
Meanings of since as an adverb: because; as; given that; in view of the fact that; while.
Meanings of since as an adverb: from the time when.
For is a preposition.
Meanings: representing; intended for; meant for; on behalf of; in place of; in support of
Examples of Since:
1. Since it was still early, Sidhesh realized that the shops would not yet have opened.
2. Smita decided to take her umbrella since she realized that the sky had darkened and it looked like it would rain soon.
3. It is always wise to leave early for an interview since traffic jams can always cause a delay in reaching on time.
Examples of For:
1. Shraboni was disappointed on discovering that the white dress had already been sold as she had intended to buy it as a gift for her daughter.
2. One must always stand up for one's friends.
3. The school headmaster explained to the new group of students that the school logo stands for honesty and integrity.