The Wood Wall is the next step up in wall based protection. It functions just as one might suspect by keeping things on one side or the other. Because there's no "gate" construction item at the moment, it is impossible to form a perfectly impenetrable wall without having to use a Hammer to get past it yourself.
Wood Walls are slightly better than their Hay Wall alternative with 100 Health to start out with but are still susceptible to fire. Adding more Twigs, Logs, Boards, or another piece of wall will allow you to upgrade the wall segment one time. This will give the wall 200 Health but it will still be flamable. For this reason, use caution.