A window will pop up for the UV Snapshot. Here you can set the resolution for the image, file type, and where you want it saved.
So under File Name, select the directory you want to save it in.
For Size X, Size Y, I typically set my snapshots to 1024 X 1024. Maya has a hard time dealing with maps higher than 3000. Don't try it.
For Image Format, I usually use Tiffs.
Once everything is set, click on the OK button. It takes a couple seconds for Maya to take the snapshot. But now we have an image of our uv's!
Before we start working on our texture maps, I usually delete the history on the model. This deletes all of the uv translation, projection, and rotation nodes. It also makes the model file smaller.
This is what the snapshot of the uv's look like in an image viewer
I typically work in Photoshop, and occasionally Deep Paint. If you're working in Photoshop, this will be useful for you.
Copy another layer of the uv's, and set it to Screen.
Then create a new layer between the two uv layers. This middle layer is where I paint my texture map. With the top layer set to screen you will be able to see the uv's and still work on the middle layer.
This is what my texture map looks like as I have been working with it in Photoshop. It is important to remember what uv's are what for painting your images.