How can i avoid paying interests.?

I have a credit card up $700 I owe $608.00 to be exact they ask for minimum payment of $15.00 I want to pay it off asap. but dont have all the money at hand. tho i can afford to pay $100.00 each month. If i do pay $100.00 each time will they charge me interests?? or what should i be doing because all i want to avoid is getting charged! im not familiar with credit cards. i got carried away swipping and now am payin the consuiquences all i know is that i need to get this big bill off my chest.