You are allowed to do up to three away rotations 4th year (Primary Care counts as a fourth if you want to do that away as well). START APPLYING EARLY (end of January to end of February in your 3rd year is ideal). It will take several weeks to months to get the paperwork in order, get your transcript sent, prove you have immunizations, etc. The process is very school dependent, with the best place to learn each individual school’s process by their particular website. Some schools require an application fee, some require letters of recommendation, others require essays; again, the best place to learn this information is on their website. If you can’t find the info, a good person to email is the program director for that specialty.
Away rotations can hurt you if you are mediocre, or don’t perform at your best (obviously). Carefully consider whether you want to risk that. For some specialties (and programs), it is basically required to do an “audition” rotation at that place. Talk to the current 4th years who are doing your specialty to get the feel of how away rotations affect your specialty as each is very different.