I am 19 years old.. almost 20..

Im not very fit and i started playign alttle football after exams and i reallized i keep geting pains and cramps for hte slightes bit of sudden movement...

So i want to start going to the gym..

do a few work outs.. get a bit toned and firm up my thighs and arms.. cz i feel a little sloppy.. am at average figer not overwieght or antyhing.. jsut not fit ..
and i dont generally do any excersise either.. so yea wil be a new start for me..

so any help on how to start off at the gym willbe greatly appreciated..

thanx in advance