What are you, personally, interested in? Where do your passions lie? What do you want to learn more about?

Try to build something, anything, it doesn't need to be complicated or awesome or even original, that scratches a personal itch. In the course of doing so, you'll gain experience using other people's code. Perhaps you'll run into a bug using their code. That is one of the best ways to get started. It's a small change and you gain experience figuring out how other people write code and interacting with the maintainers.

Or, perhaps one of your favorite pieces of software has some annoying thing it does, or some missing feature you really want. (If you aren't a user of open source software, now is a great time to start!) Try to fix whatever it is that bothers you / or you consider missing.

Above all, do not be discouraged if your change gets ripped to shreds or outright rejected. That's known as learning ;)

Since you're interested in getting attention from recruiters, let me tell you my best tip that will get your email flooded with recruiter spam: open a linkedin account and fill it with bullshit skills that sound trendy.

You'll start getting emails from recruiters within the week with the canned text:

"I stumbled upon your resume..."

Never fails brah!!

Read the issues for the repository, pick one, and try to figure out what the problem is, and what the solution is. As you progress, you can report on your findings.

It's ok to fail, the journey is the important part here. Eventually it helps you get to the point where you can actually start making impactful contributions.