To add a border, add a new layer once you finish everything else (generally... unless you want certain things over the border).
Then, do the following:
-Select -> All
-Select -> Shrink (Usually 1 or 2 pixels, but try it out to see what size you like better for what you're working on)
-Select -> Invert
-Now choose a brush or something else to color in the selected area. You may want to change the opacity from 100 to something else to make the border partially see-thru.
mmkay... well, make the text match more with the background. I just hate it when say there is a green background, and blue/red text that doesn't fit at all.
oh, and same with the pictures, they don't match/blend with the backgrounds really.