'Verb (dictionary form) + しかない' expresses the idea that someone has to do something because he/she HAS NO ALTERNATIVE. Example situation: Eric is very hungry. It's late at night and nearby shops and restaurants are all closed. He goes to the kitchen and looks for food. He has found nothing but an apple. He doesn't like it much but he is too hungry to not eat it and simply go to sleep. He is too hungry to wait until tomorrow morning. So he has no choice but eat the apple. In this case, I would say "エリックはりんごを食べるしかない(Eric wa ringo o taberu shikanai)”. Another way of expressing the idea that someone has to do something is to use 'Verb (Nai-form) + なければいけない/なければならない'. It shows that someone must/has to/need to do something.

Yes, that's correct (my wife is Japanese)