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]