1. Select your cube
2. Go to component mode, namely faces
3. Select the face
4. Right click > apply new material > lambert (for example)
5. Open attributes for the lambert
6. Hit checkered box next to color, select file
7. Hit folder icon, browse to jpeg
8. Hit 6 to view textures
9. If it looks ok, fine, done, if not: ask me about UV mapping

or better yet, do the texturing tutorials that come with maya, cause they'll give you a good foundation for the whole area. And really, it's not a zillion steps, it'll take you maybe half an hour to learn a lot.