You need to put 2x 10A fuses. One fuse is for the original circuit, the other fuse slot is for the new wire. Don't use 15A fuses, they won't fit and that tap is rated for 10A max.
For ground, pull up the kick panel (panel surrounding the hood latch). There should be a screw attached to the chassis to which a wire is already connected to. Unscrew it it slightly and wrap your ground wire around it and retighten.