before you put it in your tank, make sure you give it a good wash, boil it, and then soak it in water to make sure that all the tannins are out of it, otherwise it will discolour your water, and change the water at least every other day to avoid other nasties growing on it. Also is it hard wood, because soft wood will rot in the tank.
it pays to go read through this site thoroughly, because this topic has been covered many times, and i'm sure you will find the answers you're looking for. good luck