Makoto, if you search YouTube, "adding a sub panel" you will find videos describing what you are looking for.
The biggest challenge is knowing the correct terminology so you can ask the right questions and to find what you need.
First off you will need to have a suitable Double Pole Breaker installed in your Main Panel to protect the sub panel you are about to install.
That breaker needs to match the brand of your Main Panel, i.e. Square D or Stablok etc.
Usually a 60AMP double pole breaker is what's used but will depend on what the sub panel you have is rated at.
What brand is the sub panel you have in the picture?
As far as wire to run from the main panel to your sub panel, that will depend on distance and if you are running it outside or under ground, If it's inside the same building you can use 3 Conductor 6 AWG and that will be good up to 60AMPs, you can use 3C/8AWG for 40 AMPs.
The breakers for your new sub panel will need to be same brand as the panel.
You can then install the breakers you will need, single pole for 120VAC and Double Pole for 240VAC, you just need to size them according to what is on each circuit, standard outlets normally use 15 Amp single pole breakers.
You will need to use the correct bushings/wiring retainers where the wire enters your sub panel, looks like you have removed the knockout and just pushed the wire through, this is a very dangerous practise and should be avoided as bad things happen when wiring is installed incorrectly.
As the other posters have suggested buy a book on house wiring or contact an electrician, if you get this wrong you can get hurt or killed and worst case your house could burn down.
Please get help if you are unsure.
Regards,
David
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