What is the difference?
A terms of use governs the use of the website. The terms of use allow the users to do certain things on the website, but also a list of prohibited behaviors.
A terms of sale governs the sale of a product through the website. The terms of sale is an agreement stating the obligations of both parties.
Does a website need both?
A website should have a terms of use to access the website. If users are registering an account on the website, the terms of use may become more significant.
A website should have a terms of sale if the website sells a product.
Thus, a website should have both a terms of use and a terms of sale, if a website will perform both functions, use of the website (or registering an account) and the website sells a product. However, both agreements may be combined into one. Typically, a website will have a terms of conditions that includes all the information a terms of use and a terms of sale would have all in one agreement.