Firstly simple borders:
Simple 2px border
1. Create new layer
2. Ctrl + A [To select all]
3. Edit>Stroke
4. 2px Black [Leave the rest alone] Then click OK
Dual Border
1. Create new layer
2. Ctrl + A
3. Edit>Stroke
4. 3px White [[Or any other colour] And leave the rest alone]
5. Edit>Stroke
6. 2px Black [Leave the rest alone]
Clear border
1. Create new layer
2. Ctrl + A
3. Edit>Stroke
4. 3px Black [[Or any other colour] And leave the rest alone]
5. Edit>Stroke
6. 2px White [[Or any other colour] And set the blending mode to Clear]