Several upportunities exists
You can go for forex trading where you passively get money when people copy your trade
Affiliate marketing that is referral based can passively get you income.
You can establish a company
You can invest in real estate
The list is inexhaustive.
It is a good idea to take some courses on generating passive income.
Many don't realize, but passive income is the way to get rich. Not active income. So, improve your skills, start your work, and earn splendidly.
You don't really need a course of sorts all you need is just to go over to youtube.. okay the first step is to identify what you actually want to do.. what skill do you want to learn what is your passion and how will that will help you make money.. then when you figure that out the next step is to go over to youtube and search that specific keyword in your niche and see what pops up and watch every video that catches your eyes