A wood screw will have a courser type thread and will have a sharper point.

to screw to pieces of wood together>.<

Just exactly the same way you screw into wood.

Since tree trunks are made of wood, you can put a wood screw into them if you wish. It is always easier to screw in a screw if you drill a guide hole first.

A screw holds wood together better than a nail because the threading of a screw provides a horizontal grip on the wood. Nails are driven down into wood and have nothing but the pressure of the wood to keep them attached, which means it is easier to pull a nail straight out of a board than a screw.