Yurs, well, it looks to me like you're trying to get us to do your assignment for you, so I'm not going to go off looking for pictures to make it even easier for you. You can try drawing this out, however...
Protonation of one of the anhydride carbonyls, attack on that carbonyl by the salicylic acid -OH, pushing e- density onto the protonated carbonyl.
The salicylic acid -OH deprotonates. The other carbonyl on the anhydride is protonated.
(One of) the -OH groups on the initially reacting carbonyl centre now pushes electron density in, to re-form the sp2 centre, the leaving group is now acetic acid and the carbonyl on the ester that's just formed deprotonates to give product.
If you draw that lot out and have a look at it, you could come back with any further questions.