Magic Arena has a really solid introduction/tutorial section by now.

To get into commander i think it makes sense to find some reconstructed decks that seem interesting to you. A lot of them are very upgradable, giving you a good base to build on.

EDHRec is a great website to help you find synergetic cards

I will first say you can ask as many questions and post as many things as you want to this community and you will always get answers from people, and the questions will always be well-received.

Are you looking to just play with your child, or are you looking to play at a local store or something else? That will help us narrow things down a little.

Does black white deck where you clean the board with wrath of god then return zombies from the graveyard work?

If you are just looking to play casually at home, this deck and all deck ideas you have will be playable and fun. This tends to not do so well in the current formats, but there is a deck you can play on Arena in the Historic format that you might like. Search for "Historic Orzhov Zombies", and here is an article and video from 2021 about the play style: https://www.mtggoldfish.com/articles/historic-101-orzhov-zombies

How do you play with two sided cards? Are they just for sleeves?

There are a few types of two sided cards, sometimes referred to as MDFCs (Modal Dual Faced Cards):

1. Lands, like Clearwater Pathway let you decide which one to play at the time. You would pull the card out of its sleeve and switch it if you want to play the back side.
2. Spell-lands, like Kazandu Mammoth, let you play either side as well, except one side is a land and one side is a creature or spell. You can only pick one.
3. Saga creatures, like Fable of the Mirror-Breaker, you must play the enchantment (front) first, and then after the saga finishes its lore counters, you flip it over and put the creature into play.

There may be more types but this is a good primer.

Where to get informed? What works now? I see more people are playing chilled, for a difference back then you would get obliterated.

I would suggest starting with Youtube videos, and search for things like "Metagame overview for new players" or "Meta decks for returning players" or something like "2023 Standard meta overview". The videos are extremely helpful I find. You can also search for "_____ Deck tech" where the blank is the type of deck you are curious about. Like "Orzhov zombies deck tech", and sort videos by newest.

The next best place is your local game store. These stores are wonderful places for educating people, and normally filled with other players looking to help and looking to expand their play groups.

How do you play with two sided cards? Are they just for sleeves?

99.9% of people I've seen playing Magic in the last 15 years or so have sleeved their decks, even if the cards aren't worth very much. So yeah, sleeves with opaque backs are what most people use. When it's time to flip the card to its other side, just take it out first.

However, if you prefer not to sleeve, you can use a checklist card. They look like this:

https://scryfall.com/search?as=grid&extras=true&order=name&q=checklist&unique=cards

You check the box to show which card it's representing, then put the checklist card in your deck at the start of the game and leave the double-faced card off to the side. When you play the checklist card from your hand, then you replace it with the double-faced card, and use that until the card goes back to your hand or library.