Sometimes if I change from RGB to grayscal mode, or vica versa the selection line goes away, but not always. I even opened a new canvas and the selection line is around it. How do I get rid if it?

What you are seeing are not selection lines, they are layer boundaries. If you don't wish to see them you can click View and uncheck Show Layer Boundary.

Keep in mind that if you turn that off, you may not be able to understand why you can't paint or put color in part of the layer. You can't do anything outside a layer boundary.

The image shows the layer boundary on one side and with the boundary hidden on the other. Both layers were filled with paint.

I get it. Thanks.
The layer boundary is on the outside perimater of the image so it will not be a problem. I knew it had to be something under "view" but I only tried what looked obvious.
Thanks.

One more thing, that's sort of important to know. Sometimes, like when using bump maps or displacement mapping, the layers have to be the same size as the layer being mapped, so you would right click the layer that you are using as a map and click "Layer to Image Size". Failure to do so, would result in the layer not showing up in the selection list for mapping.

Although I have tinkered with some advanced stuff (following tutorials), they is not my interest or abilities right now. But I will keep it in mind.
Thanks