once you've exported your object into sandbox, open the material browser and select the objects material by using the eyedropper [see below]. you can change the texture file by clicking on the folder next to the channels.
The diffuse channel is the standard texture file which represents colour. By expanding the + box next to diffuse you will have options for tiling of the texture. This tiling will be reflected throughout all of the other channels.
Normal mapping is a technique used for faking the lighting of bumps and dents. Normal maps can be created in photoshop either using the nvidia dds plugin (file/save as/*.dds) or by downloading xNormal and using the photoshop filter.