If this all sounds confusing, and you haven't done something like this before, either just take it one step at a time, or have a competent installer do it for you.

At the point you have attached the new fuse panel to the car (one swtiched power lead, one "always on" power lead) you just put spade connectors on each power lead for each device and attach it to one slot on the fuse panel. The ground wire goes to a solid metal ground point.

If your device comes only with an accessory plug (cigarette ligher) you can either cut off the plug and wire it directly, or instead, wire in an accessory plug to the fuse panel and just plug it in.

For those devices that come only with an accessory plug, I use the accessory plug because it preserves the original wire for the accessory, allowing me to later simply unplug it and move it to another vehicle. I use a sealing tape to assure that the plug stays in the socket. I have had my GPS devices wired into my Jeep this way for years and it works very well. Recently I upgraded GPS units and simply unplugged the old one and moved it to another vehicle.

For the stereo components that don't have accessory plugs, I connect them as described. They're easy enough to disconnect if I sell the car and want to keep them. In fact the whole fuse panel just comes out without leaving any sign it was ever there (except the rubber plug on the firewall).