Tire rim for plymouth sundance?

i drive a 1992 plymouth sundance and apparently i need a new tire rim for my right tire. i guess if i dont fix it soon it could mess up my transmission or something. my step dad is leaving it up to me to find one, but i need to know if theres certain sizes or something? can i order one online? buy one at the auto section of walmart? i really know very little about cars so anything you can tell me would be great. thanks.