so how exactly does tin and copper work?

[KeiKei]

like i found 2 big tin veins in 1 cave

and i know you cant find both in the same vein

but can you find both in the same cave?

can i find both in 2 caves close to each other?

or do i have to travel for a long time on boat or something to find a big copper vein?

[Shadow7168]

It's more or less random, though tin is generally more common than copper, since the copper ore(atleast on l1) also has iron in it.

[Sevenless]

Think of the world as a giant grid. Randomly speckled into that grid are metal veins. Some are more common (tin) while others are quite rare (gold). Whether your cave intersects no ore nodes, or three is random chance. You should be able to get rustroot and use the prospecting system to find nodes from the surface. If you figure out roughly where it is underground, you can mine to it. Alternatively, you could build a minehole right above it and have direct access. In past worlds I advocated attempting to mine for it randomly, but the improved prospecting system makes it quite easy to use and it's easy to get started.

[MagicManICT]

I still dig randomly starting out as I can usually get access to metal faster, then, than I can get access to rustroot.

Just watch out for cave-ins if you do start out mining randomly. They're a real headache.