Both means "can not/do not see/watch." Depending on what subject word you put before the words, it will be applied to 1st/2nd/3rd person. 1. Minai (見ない)=>Informal (the ~nai at the end makes a word informal) 2. Mimasen (見ません)=>Formal (the ~masen at the end makes a word formal) The use of informal and formal in Japan/Japanese is very important so if you want to know more about it, I will tell you... Hope my answer was helpful. If you want to know more or are still confused, ask me! ^_^

"ません" is a negative form of "ます". Therefore, "見ない" is a simple negative form of "見る". "見ません" is a negative form of "見ます". As you may know, the suffix "ます" or "ません" makes the verb more polite.