I quote from one of my other answers.
"To use the bench, you must place it as a hotkey in your inventory. To do this you must press ESC on your computer and move the bench to the top row. Press ESC again and then either click on the bench [or press the number corresponding to the hotkey placement of it] and click on the ground where you want to place the bench."
To actually use the bench, stand quite close to it and press ESC and it will open up the crafting menu.