First you install Git on your system (if you not already have that) - an easy way is to use the desktop client: https://desktop.github.com/
Then you create an github account here: https://github.com/
Check the documentation on github desktop : Creating your first repository using GitHub Desktop - GitHub Docs
That way you dont need to use command-line stuff (thats what people normally fear) - instead you use a desktop application that is (in my opinion) way easier to get into.
Basically you create a new repository (as far as i remember, it can be an already existing directory, for example your vault) - git will install some files there to be able to connect and monitor.
You can then Push/Commit and Pull from the desktop app, but this still is some friction.
If you followed the steps to set up everything via the desktop app, you can then make it simpler for you by Installing the community-plugin called “Obsidian Github” from within Obsidian. You dont need to authenticate, as this is done already through the installation process and registering your directory via github-desktop app (the additional directory and files that got created in your vault)
You should make a .gitignore file in the root of your vault, but this is explained in the documentation from the plugin (its to exclude some system-files from constantly updating to git)
You set the backup interval in the plugin page (every hour, or once a day or whatever you feel comfortable with) and thats it.
You will see a message in Obsidian when files got pushed to git and you see in the lower part of Obsidian a status message what the plugin is doing, and when the last time was it pushed/pulled changes…
I know its sounds a bit complicated at first, but with Github Desktop its easier as you dont need to fiddle with command-line prompts.