To install Steam on most distros with popular DE's, you click the software store to open the software store. If Steam isn't listed in the front page then just click the search box and start typing Steam.

When you see it, click the install button.

When it is done open it by clicking the Open button or pressing the Windows (or Super) key and type Steam. Click it when you see it.

That experience is highly dependent on the Linux distro you're using. Steam comes preinstalled on gaming-centric distros like Nobara or Pop!_OS. More "general purpose" distros like Mint or Ubuntu might require adding an apt repository before you can install steam from their GUI package managers, but adding an apt repo can be easily accomplished with a GUI as well.

Basically, if there's no guide for installing steam for a given distro, or the process of installing steam is more than a couple easy steps, that specific distro probably isn't well suited to run steam.

Weird, I would expect Steam to be in the Ubuntu repos (assuming that's what you were using, since you mention apt), but maybe not. As for apt, or apt-get, they are just the terminal equivalent of the GUI package manager (synaptic? it's been a minute since I ran ubuntu), so if something isn't in the repos, apt at the terminal won't find it either. If it's not in the repos, you should be able to download and install steam from the website just like you would in windows. It gives you a .deb file which will launch just like an executable installer in Ubuntu. But to your point, yes, sometimes things in linux take a little extra thinking to get to work. Getting accustomed to the way Linux works can help overcome hiccups like this. Windows has many quirks as well, it's just that if you use WIndows often you know your way around them.