Glad you’re here. I just got my Open Water last summer and can assure you that your training class that you need will walk you through all these questions/problems. You can also find most everything on YouTube but its still vital to have an instructor with you to show/watch you and as a safety monitor. Besides, you’ll need the certification before anyone outside of Mexico will rent gear and fill tanks for you.
Depending on where you live, you may have some very reasonable priced classes near by.
Best wishes. Bill