Well...just about everyone knows more about electricity than I do so, this is just from the little experience I have had re wiring two boats that I have and doing some wiring here and there to add lights, aerator pump etc...
On my bass boat, I have power coming from battery through two 8 gauge wires to my fuse block (with blade type fuses).
The size of your fuse block (how many fuses you have) will depend on how many things you want to bring power to. The size of your fuses will depend on how much amperage these accessories will draw (i.e a bilge pump can draw 15 amps while running lights will draw 5).
So, you have two 8 or 10 gauge wires (size of wire depends on how much power you need to run and the distance of the wire). You can find charts that have standards for different size wire ratings etc... online or library
In this power from battery you will want to have a MAIN FUSE...usually 50 amps. This way, if you have a short at the fuse block, the main fuse will pop, saving a fire, your battery, accessories....
From the battery to main fuse to fuse block. Fuse block on my bass boat is a 8 fuse block. When you buy a fuse block, it will have marked a positive post where you attached the main power from the battery...this will bring power to all the fuses in the block.
When you get the fuse block, you will see where you place the fuses (whether you get the blade type fuse block or the type that takes the glass tube kind). You will also see where you attached the HOT leads (wires) going to whichever accessory.
You still need to GROUND all of this otherwise you will not have a complete circuit.
From the fuse block you will see where a NEGATIVE wire goes and this will eventually go back to the negative side of the battery. (or will join up with the big 8 or 10 gauge wire from the negative side of the battery...black wire).
You can ground this in more than one way...just make sure you always have a good ground. A bad ground accounts for almost all of marine electrical problems.
The way I recommend you ground this stuff is have a "grounding board". Not sure if thats the best, or official name for it. It is where you will ground each accessory from the fuse block. This can be done with jumper wires (individual wires for each accessory circuit). This way, each circuit has its own ground....giving everything a good ground and, if you ever have problems you can check your ground for each circuit at this one location.
The negative 8 or 10 gauge wire from the battery will come to this "grounding board", therefore finally grounding everything, completing the circuit.
THis part is confusing to explain and harder to understand. Ill post pictures of what I have in the bass boat