First you need to layout your UVs using the UV Texture editor - basically you need to lay them out flat - then you take a UV snapshot under Polygons > UV snapshot. Save the file as a targa.

Next open your snapshot in Photoshop - it should be saved under images in your project folder (Make sure you set the project before taking the snapshot or it will be saved under your default or last set project.) Paint your textures in Photoshop - save a photoshop file of your textures and a save as targa file.

Go back into maya - apply a shader to your model, click the map icon next to color and pick file from the new window. Browse for your texture file, select and your textures should appear on your model.

Hope this helps.