can u put poison to arrows?

Yes, yes you can.

.... how?

Equip a bow. Select a poison from your inventory. You'll be asked if you want to poison your bow/arrow. Viola!

what would poisoning my bow do...... when i touch the bow i get poisoned? x.x

Erm, no. IIRC, the game asks you to poison the bow, but you're technically poisoning the arrow. Your next shot will then carry the poison's effects along whatever damage the bow + arrow would normally do.

Just one arrow? What about when you poison weapons, does the poison on them also last only one hit?

yep