Where do waves come from?
Often the wave you are riding today was generated many days or weeks ago and from a long way away -sometimes from halfway around the world! Though some waves are created just off-shore, maybe just hours before you rode it. Most surfers prefer the long period swells generated more than a thousand miles away.
All that energy heading toward the shore has to go somewhere! Though much of a wave's energy dissipates after it breaks, some of it returns back out to sea. This happens in the form of currents. When these currents become organized and concentrated, they are called a rip current. A rip current is basically water piled up on the beach returning to where it came from.
As a general rule rip currents don't travel far to reach equilibrium, so they dissipate relatively close to shore. Knowing this, don't waste energy by fighting the current while trying to swim directly to the beach. Keep calm if you are caught in one and swim parallel to the beach. Before too long it will release it's grip and you can swim back in to safety.
Yes, surfers, bodyboarders, and bodysurfers can be territorial. And yes, the ocean belongs to everyone. The best advice is to be respectful of the beach and treat it as though it is a precious resource, which it is. Most of the obnoxious territorial surfers are going to be at advanced surf spots, and those are spots you won't be bothering with anyway if you are a beginner. Often these are hard to get to places, though some are in plain sight.
You may not be aware of the fact that you are at an advanced surf spot. Unlike ski slopes there are no posted grading signs. Be friendly and courteous, advanced surfers with any character will be courteous right back to you. If it is an advanced spot you have stumbled upon, they will let you know -usually politely and informatively and will suggest a better place to learn. The good news is that most bodysurfers are willing to share their bodysurfing spots and are happy to see a new face in the water.
If in doubt, and if there is a lifeguard nearby ask her.
Once in the water there are some basic "rules" designed to keep everyone safe and happy.