Although they are named sugar cookies, these cookies in reality aren't that sweet. These cookies are usually made for special occasions so they can be designed with different designs and they can also be made in different shapes and sizes to reach a specific cookie wanted. Sugar cookies are also sometimes topped with frostings to add a bit of flavor, sweetness, and color.
If you want a sugar cookie recipe then go here.

Christmas Cookies are usually just sugar cookies, but just with a design or shape pertaining to Christmas. They can come as Christmas trees, gingerbread men, gifts, Santa Claus, reindeer, and many more shapes.
Here is a Christmas cookie recipe of a Christmas tree: recipe

Another popular Christmas cookie is the gingerbread cookie and they are known to be good for house building and people building (cookie wise, of course).
This is a good cookie recipe for making gingerbread cookies for Christmas: recipe.
