You gonna need : 

Leather straps (or you can use your old belt)

D-rings

Key rings

Swivel Hooks

and 

Sewing kit / Sewing Machine / Hot Glue (add.)

For this project, I recommend you to sew more than using hot glue. Once I made a camera strap, and it broke after a week using it, because it just not too strong. You can use hand-sew kit or just use a sewing machine.

1. decide the length that you want for your strap. Because I'm making a hand strap, the length that i need is just around 50cm. don't forget to leave some extra cm for the folding over. I add 2 cm.

2. put the d-ring inside and fold the end of it. 

3. SEW IT. (CAUTION: be careful, because it's quite thick, It could bend your needle.) do it on the both sides.

4. next, attach the hooks into the key rings. then, attach it to the camera.