Hi, i hope i can help,
A lot of the information you may want might be here :
Packaging Unreal Engine Projects | Unreal Engine 5.3 Documentation
Also when your ready to try get your game on steam, you need to do so via steam`s ‘Greenlight’ process. This is where you submit your information about your game such as videos and descriptions where steam users can look at that page and then vote to get your game on steam, once you get enough votes (which we dont know the number of) or valve decided they want your game on steam, then they will start working to get your game actually on steam. The whole steam greenlight process is going to cost you £70 ($100) , but if you want you can add a ‘Concept’ of your game aswell which users can also view, for no cost so you can get free feedback. Anyway, back to greenligh, you can find information on it here :
Sometime in the process if you are successful with steam greenlighting and get accepted, you may want to consider intergrating steamworks into your game with the steamworks sdk. This will allow you do things such as add achievements to your game and other steam things, but this can be done much later in development. You can find information on steamworks here :
And, to put it online, after your down packaging i believe you could just upload the files to a site which allows users to download them and run the game themselves. (Although please correct me i am wrong)
I hope this helps in someway. Also if i am wrong in places (probably am) then sorry, and please if anyone can correct it would be appreciated.
Hope it helps!
Lawrie.