Since is used for past tense and for is used for present tense
eg: since he was tall he sat in last bench                    
      he made it for his teacher

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"Since "  is used  to specify a point of time in the past.    Since is also used to mention a reason or a cause.

"For" is used when we mention a duration of period and not a point of time.  For is also used for telling the reason of doing some activity.

Since:           I have been in this city since 2010.
For          I have been in this city for the last four years.  (2010-2014)
                 here, duration of 4 years is mentioned.

"Since"  is used for telling a reason.
       I traveled by an auto since the bus had not arrived in time.
For :    I prayed God for the good of my family.

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