1.
to be the explanation or cause of sth
SYN explain :
The poor weather may have accounted for the small crowd.
Oh well, that accounts for it (= I understand now why it happened) .
2.
to give an explanation of sth
SYN explain :
How do you account for the show's success?
3.
to be a particular amount or part of sth :
The Japanese market accounts for 35% of the company's revenue.