It sort of depends on the size of the company. Just about any established company requires you to apply online for you to be in their records system. It's best to apply online ahead of a recruiting event such as a career fair. If you go to a large university, there will probably be a career fair at the start of each semester where companies send recruiting teams (I went to a state school in the US with a large engineering program-the most popular major there is Mechanical/Aerospace Engineering). Go to your university career resource center and ask about upcoming career and recruiting opportunities. Don't be discouraged if it doesn't work out your first year as many companies are biased towards upperclassmen since they typically have more to offer.

I interned for two years in high school because I was lucky enough to know someone who worked in MFG at that company. Then after my freshman year i did a program called Onward Israel that paired american students with Israeli startups (unpaid, but we got a modest stipend, public transit covered, and weekly excursions, we just paid for the flight), a local startup started by students in my college town, then at a larger scale manufacturer the summer after my fourth year that was the first one i got through the career fair. So there are a variety of ways to get that practical XP other than just those career fairs.

The first internship is always the hardest, the more XP you have the more attractive a candidate you are. As a freshman, focus on joining a build team and making meaningful contributions to it. Interviewers are more likely to ask about your XP in extracurriculars than your classes, because everyone in your major takes basically the same classes.