About facebook ads

Hey guys, i want to learn facebook ads as a skill. But im wondering, how can i start practice? What can i sell with it?

I know there are tons of ideas of online business, but somehow facebook adds seems interested for me, that's why i want to start it.

However, i don't have a bid budget for that, like only 100$ / a month or so to invest, is it enough just to start?

If you want to learn to run a business,
Then Google maybe enough,

If you want to learn to run an agency,
Then you need learn
Advertising as a whole and not just Facebook
You may decide to narrow it down to digital advertising,
Which includes many platform and many channels across multiple platforms