What I don't get...

[Buffalobiian]

So do I have to use every single number?

I mean, I can do 25 - 6/6 = 24

And can I combine numbers?

like 256, 68 etc?

I'm suspecting you can, since if he's intentionally saying "you can only use about three signs, since there are four numbers", he's telling you the maximum, as there are 4 numbers, but didn't clearly say to use 3 signs.

Edit: What about powers? If you use pen and paper, 8^6 is written without a "sign".