That's the motto of the Brady Oyster Company (and others around the country) and they sell bumper stickers!
Yes, you need a shellfish license to harvest oysters, clams, mussels, cockles, crabs, shrimp, lobsters as well as seaweed. The license costs $18 per year. Seasons and open harvest beaches vary throughout the year for each type. Oysters have the widest range of season compared to clams and crab. There are limits for each type of shellfish, counted per day.
Before going out shell-fishing for anything, I check the fish and wildlife website to make sure there hasn't been a closure for red tide, PSP (paralytic shellfish poisoning), or other reasons, like allowing the shellfish population to come up again on that beach. I check when low tide is and make sure I arrive within an hour either side of that time. It's very disappointing to arrive at the wrong tide!
The old adage "only eat oysters in months that contain an 'R'" was a crude way for people to remember when oysters are likely to spawn, which is in the warmer months, generally. It isn't that you can't eat them during spawn, but they're not as big, they're watery and flubby and the liquor is milky. In some areas of the country, warmer waters also mean higher possibility of PSP or red tide. It's dependent on location, water flow and temperature whether oysters are good to harvest at different times of year. Because Pacific Northwest waters are so cold year-round, I've eaten delicious oysters in May and June. Same goes for Nova Scotia, Maine and the excellent Prince Edward Island oysters.
As to shucking ... in the drawing above, you see that the "hinge" is to the left of the picture. It's where the oyster is attached so that the oyster can open and close to feed and regulate body temperature. That is where you want to open it. If you try to open it at the "lip" end, the shell just continually chips away, there isn't anywhere to get a good bite to start opening the shell. At the hinge, there is a divot between the two shells where you put the tip of the oyster knife, push hard, kind of waggling a bit until you feel the tip break through. The juice will start to run out at this point - don't waste it! Most beginners try to pry the oyster open by twisting the knife back and forth. It works, but it's a lot harder. Better to pry up and down. Once the oyster is open a quarter inch or so, you slide your knife along the top shell, as close to the shell as you can, to cut the attachment on that side, allowing the shell to fall away. Now your oyster is in the "half shell" but still attached to that one. Again, slide the knife gently under the oyster and cut the attachment. That's how you'd be served oysters on the half shell. Or you use it in your cooking and toss the shell. It takes some strength, but when you get the technique down, it isn't a fight.
Choosing which ones from the beach might be easiest to shuck gets to be clear once you've learned to shuck them. I look for a clear hinge, with a divot. Sometimes, the hinge is almost fused, with nowhere to put your knife. Those are frustrating, though not impossible. Also, if the oyster is in a cluster, some may be easy to get at, others not, due to how they attached to themselves or the rock they're on.
With oysters of different types ranging from $8 to $14 a dozen, it's worth it to go out for your own. Even if I only go three or four times, I feel I more than paid for my license. Plus, I go for clams, mussels and seaweed, too, so very worth the $18 license fee. Plus, I get to be outside, smelling sea air, watching birds and gathering food. Can't get much better than that!