Well, it's a little hard to say without more context, but here are some examples:
Usually, "I don't care" = "no me importa." i.e. I don't care if he comes (No me importa si viene) But if you say "I don't care about her" it's more like "No me interesa ella"
"It doesn't matter"= "No importa" or "me da igual"
"I don't mind" = "No me importa" or "No me molesta"
I think that's how you would say those expression in Spanish, but again, you really need more context..