new layer select>all>select>modify>border>(# of pixels up to you, but 1 is the most common)>edit>fill>(color,pattern,w/e)>ctrl+d
That way makes it semi-blurry. Just do: New Layer > Edit > Apply Image (Normal settings) Ctrl + A > Edit > Stroke > 1 px black (normally).
yup, or if you want to make borders with multiple edges, do something like: New Layer > Edit > Apply Image Ctrl + A > Edit > Stroke > 4 px black (click OK) Ctrl + A > Edit > Stroke > 3 px white (click OK) Ctrl + A > Edit > Stroke > 1 px black (click OK) so you have three borders on top of each other, all on the same layer, then set to something like overlay or softlight