This is sad but....
 

This is truly sad of a pirate like me but on the test server you don't get many active people. So, how does 1 solo board a ship?

Well, I don't have any access to the test servers; but, assuming that the mechanics of boarding a ship are the same for both servers, then it works the same as boarding with a crew (i.e. you fire on a ship until it's out of hull points, green circles show up on the side of the vessel, you fire grappling hooks into those green circles, the "Board" menu pops up at the top of the screen, you can either wait to try to take out masts or troops on the other ship, or you can press the "Board" button and swing over to the other ship).

Of course, once you're over on the other ship there's no turning back and it can be tough...even deadly, and when you die aboard the enemy ship your ship sinks. It's best to start with something low level, like the Bulwark flagship between the Devil's Anvil and Tortuga, or the Navy Panther off Driftwood, or the EITC Sentinel off Padres Del Fuego.

In general, Navy targets tend to be have slightly lower level mobs standing guard.

EDIT: Oh, and while your ship is safe while you're on the other ship, keep watch of what else is out there on your compass because ships may be right on top of you when you swing back to your ship if you're not careful about where you park.

I thought all I had to do is stop right by them and then get out a grappling hook XD

thanks I'm still confused about the actual "BOARDING" part but I'll give it a try

Well, you usually do have to be at a cannon, hit 8 or however you normally get to grappling hook, and then fire at the green circles. You really only need to connect with 1 grappling line and your ship will start reeling in the other ship.

The actual boarding part is a menu that pops up at the top of the screen, with a countdown timer, the type of ship, and then a button in the lower center that says "Board." Just press that button and you'll swing across to the other ship automatically; you have to kill everyone on the other side, and then you'll swing back to your ship automatically too.