installing electrical boxes for out door light fixtures
If you are wanting to install a wall sconce, you need to install one that is rated for outdoor use.

Note: The shape box you need to use will be dependent on what fixtures you would like to install. Some fixtures need round boxes while others require a rectangular box. My examples show round boxes, but this is not the only choice.

Aside from being constructed for outdoor (ab)use, outdoor rated fixtures typically include a foam/rubber gasket, a specially designed fixture base, or some other means for ensuring water resistance. Additionally, in many cases, you should use silicone caulk around any possible points of water incursion (if possible).





Some fixture bases come with extra holes for mounting flood lights. These extra holes should be plugged and then caulked around the seams.
Note the fixtures are installed in the side holes, and the hole in the middle that has been plugged.





It is also good practice to use wire nuts that contain silicone sealant, known as weatherproof wire nuts among other names, or to wrap normal wire nuts in electrical tape. This provides an extra layer of moisture defense for your electrical connections.