Upgrading steps are not clear to frontend n00bs

Hi there,
I was lost at the steps on https://docs.bolt.cm/3.1/upgrading/updating.

In step 3 it says to "Make sure you have Composer. If not, get it here".
Could you add a step / link to an explanation on how to check if you have Composer?

I am just a dumb frontender trying to install my site. I do not know what Composer is, but if it helps Bolt work, i'd gladly use it. But I wouldn't know how to check for it if my life depended on it. More, since the other steps are really clear ( "Look for a file called composer.lock"), it would make sense to keep this clarity in all instructions. :)

thx!
A