Shinakute is the TE form of 'Shinai", which means to not do/don’t do. TE form is a little hard to understand and is a seperate topic, so I won’t explain here. Ikemasen is literally “can not go”/“can not be”. --Shinakute wa ikemasen is basically like “it can not go if you don’t–” ~ basically like saying you have to. if you say watashi wa benkyou wo shinakute wa ikemasen, it means “It can’t be if I don’t study”, basically meaning “I have to study”. You don’t need to use wa/ha (ha becomes a particle so it is pronounced wa) between shinakute and ikemasen, which makes it less formal. You can also turn ikemasen into ikenai, making it even more casual. You can also say “shinai to ikenai” (or just say “shinai to” as a shortened form), an even more casual form.