Ohh damn.. awesome job on your first game bro.. that's very impressive..about the web build it's pretty simple..you can check procedure on youtube....since it's a 2d game.. you shouldn't face any issue and it will be straightforward hopefully..
To explain it roughly
Go to build settings / build profile in unity
On left side there is platform select bar
Choose webgl/web build..
There will be a 1 time mandatory module download
Do it..
Click build....
You will get 3 files after it is done..
Compress them directly into a zip ( don't put inside a folder.. select those 3 files directly and click compress into zip )
Upload on itch..
When you upload on itch make sure..
File kind ( kind of file ).. on itch upload is set to HTML..
And Tick the box stating This file will be played in browser..
Also there is a option for Embed in page - set it to manual
And set viewport dimensions to 1280*720
That's it...
HERE IS PERFECT VIDEO FOR YOU :-
It gives full workflow.. and it's very easy.... It will give your game much more attention I think since it's easy to play...
All the best on further projects