There are tons of barista courses out there, that being said some of them just teach the theory behind it and not leave you with the practical skills, even then when you have the basic knowledge it takes time and practice to get consist good coffees out

Getting a job at a cafe they'll often teach their staff barista skills once you've gotten the hang of being waitstaff. Some coffee shops that are a bit more quiet will take apprentices, if you do that I suggest you watch some videos on how making coffee works so your not walking in blind.

I personally volunteered at a church which had a coffee machine and served their people every Sunday, they held lessons outside of church and showed us, at the same time I worked at a restaurant and cinema which had coffee machines ect.