https://www.bcae1.com/
this is a website that lots of people use when installing aftermarket audio such as hi power amps, speakers, subs, etc., in automobiles. Boats are 12v as are cars as they depend on the battery for the electricity. this should point you in the right direction as it explains car electronics in pretty simple terms, not always but helps. Boats are alot more simple in that there are no seat belt sensors, engine sensors, airbags, all the electronic monitoring stuff everyone has to have. To install electronics in a boat, navigation lights and depth finder/fish finder, is fairly simple. You need to install a fuse on the main power wire (the post with a +) close to the battery so if something goes wrong, the fuse will blow and cut the power to whatever is causing a problem. Run a sufficient size power wire to maybe a fuse block/distribution block, and a ground wire as well from this fuse block to the battery. This could be where you would connect all of your electronics wires to rather than running the wires for the lights straight to the battery. Connecting lights directrly to the batt means they would be hot all the time and on all the time if the light pole, you would need to install a switch in most cases for lights. Red is normally for the hot or positive side, black is for ground (-) post. then you run the wiring from your electronics (lights/ff) both + & - wires to the fuse block. make sure you keep the + & - wires connected to the correct side (+ to + and - to -) or you'll burn it up. Post up what type of boat, where the battery is located/installed and what you want to install. the guys here will help with ideas and links on how to do what you want done.