Here are links that show basic wiring inside a breaker box.
Please look at the images.
If you need more help, answer back and we'll go to the next step
15 amp breaker connects to 14 gauge wire
20 amp breaker connects to 12 gauge wire
30 amp breaker connects to 10 gauge wire
Home Depot and Lowes have a breaker and wire size size chart next to wire cutting machine
These stores have guys who know the basic breaker size for your big appliances
Each appliance has a name plate showing wattage and voltage.
The wattage tells you what size wire.
The voltage tells you what size breaker and whether you need a 120V breaker or 240V breaker.
To lay out your home wiring:
The kitchen microwave needs a 20Amp 120V 'dedicated' line that goes just to the microwave.
The rest of the kitchen plugs are served by another 20 amp 120V breaker
When laying out rest of house, figure how much wattage might be used in an area.
For example the den might have a big 500Watt TV, and 2 ceiling fans and 4 lights.
Add up the wattage and decide how many plugs and switches you want on each breaker.
Now let's say you have a 20Amp breaker which can carry 1920 Watts for the den.
Inside the breaker box you have a 12 gauge wire for the 20 Amp breaker.
The 12 gauge wire has a black, white and bare ground.
The black connects to breaker. The white and ground connect to Neutral busbar.
The 12 gauge wire leaves the breaker box and goes to the first box in the den.
This box is your junction box.
The junction box can be a switch box or a ceiling light box.
You cannot have any junction boxes that are covered by drywall.
Junction boxes must be accessible. All boxes must be accessible.
For example, you choose a ceiling box for your junction box.
The junction box is also the same box your ceiling light connect to.
From your junction box, you branch off a wire that goes to next box.
And then a wire branches off next box and goes to next box. And so on.
If you need more help, answer back and we can help.