Ok, here's a quick primer to PSOing :3
If you just go down to the planet without a mission you can do free-roaming mode in which you clear your way through the world, popping open boxes for loot and killing monster/pressing switches to unlock doors until you get to the boss which when killed will leave behind boxes full of goodies and a teleporter back to Pioneer 2. The order of the locations also kind of shows the level progression so if you're a brand new character I'd stick to forest until you manage to kill the dragon (which is roughly about level 5 I'd say) It works very much like Diablo in that sense.
When you get to higher levels you'll want to try harder difficulties than normal because you get much better loot and the monsters are more challenging, with some interesting changes taking place at the highest difficulty levels like ultimate which completely swaps out the monsters for new ones :3
Anyhoo, let's cover some basic controls and stuff now
In the bottom right of the screen you'll find what's known as your 'palette' which is basically a description of what your 4 face buttons on a joypad will do and you should ideally correct your button binds to match (on the 360 in default binds, the left and right buttons are inverted for some reason)
Your default ones will be the same as you see in this picture:
So, at the bottom of the palette you have 'normal attack' which will swing your current weapon. This is the fastest and most accurate weapon attack you have.
When attacking, if you press any attack button while in the last bit of your swinging animation, you can attack immediately again. You can do up to 3 attacks in this manner. Each attack in a chain is more accurate than the last, so if you're fighting a creature that you see 'miss' float off a lot, it's often better to start swinging before they're in range so they walk into your 2nd or 3rd attack instead.
Now that we've covered that, let's get back to the palette and begin with the left-most button which is set to 'heavy attack'. This attack has the same animation as a normal attack but is delayed by a charge-up effect at the start, making it take longer to swing. This attack is also much less accurate than your normal attack so it's usually better to chain into it than to try and start with one. Why would you use heavy attack with all these problems? Because not only does heavy attack do more damage, but it also causes more knockback on enemies as well, which can sometimes give you the breathing space you need to recover from your swing instead of taking a retaliatory swipe to the face from the monster you just hit
The right-most button will be set to 'monomates' which are an item you can buy/pick up that replenish your health when consumed. You start with 5 if I remember correctly, but you'll sometimes find them in boxes as you explore and the green shop on pioneer should sell them. Later in the game you will find dimates, which heal even more hp and later still you will find trimates which are a full heal regardless of how much HP you have. Items stack up to a maximum of 10, if you try and pick up any more when you already have 10 of that item it won't let you.
So, that's the basic palette covered. The important thing to know is that you can change what the buttons on the palette do by going into the menu (click in the right stick on your pad to access this) and selecting 'customisation'
Also important is that you'll note there seems to be a little thing just under the palette saying 'ctrl'. This is a palette switch function that gives you access to a second palette while it's held (so holding down ctrl or whatever button is set to switch palettes will change what your buttons do to the second palette.) this allows you to have up to 6 different buttons to play with via a combination of the bottom 3 face buttons and holding or not holding the switch button :3
I skipped over the top face button because this is locked to certain functions. The normal top button is a chat shortcut that brings up the universal chat system. It's not super useful considering we all talk english on this server
If you press the left-most face button while it's up though it'll switch to the symbol chat menu and you can pop up silly pictures other players will see.
While holding down the switch button the top-most face button becomes the infinitely more useful fast acess menu. From here you can use items, switch weapons or use a technique. handy for anything you don't have on the current palettes. The switch palette button will cycle through the 3 different quick menus and pressing the top-most face button will return.
Last but not least is the number shortcuts that take up the bottom of your screen. you should be able to guess how to use these, but how you set them isn't well explained so here's a quick guide: Go into the 'customisation' section as always, select any of the palette spaces and then with the attack/ability/technique you want highlighted, press the number button you want it assigned to and you should see that number appear on the ability/tech/whatever to indicate it is now bound.
While there's a lot more to cover than this, it should hopefully give you an idea of how it works at a basic level :3