Collect crystal as much as you can and use them with Collectopedia

They will give your character 2 BP with one slot with star icon, and two more points if you successfull in collect one row 

So just to clarify, if I want to equip my character with a different kind of weapon, like a raygun instead of an assault rifle, I have to change classes?

And if so, will this affect my Arts?

You have to change classes, yes.  But after you fully level a class and master it, you can use the arts and weapons tied to it with other classes, iirc.  However, some arts are tied to weapons and won't be able to be used with the new weapons. 

Ah, okay.

That's kind of annoying. I want to try out different classes but I don't want to have to spend 10 minutes rearranging my Arts every time.

Yes and yes.

In fact, you'll have to learn new arts. Before changing I had 6 arts and after only 4.

I need to get my first Skell ASAP to fight with these alien bastards

Finally got it! That European limited edition is so pretty. I'll play it tomorrow though, right now I'm just really tired.

but once u mastered a class, u dont need to change it to the specific class to equip that weapon. For example, once u learned dual blade u can equip whenever u want, but u can only use the arts that are available for dual blade

I beat it in my first tried

Anyway, some random picture

Yes, you can.