I am using aws as learning. But i have no knowledge about billing. suddenly i saw aws billing dashboard Amount charge please remove this amount because i am a student. I have no money to pay this bill

i am using this account not so frequently but used some times in previously when told me not so much but yeach used a bit of this service and now its showing billing of 1dollar now tell me why is it and is this for? i am shocked i haven't used this service from a while and now this morning i have got this mail and then its showing me the billing of 1. and also i want to enquiry about the one dollar bill on which type of aws service that it has been made for?