A registered voter's name, address, year of birth, and phone number (if given by the voter) is public data. Which elections someone voted in is also public, but how a voter marked their individual ballot is never recorded. Ballots are always secret.
Although the data above is public, it is not available to anyone who asks for any purpose--it is restricted to certain people for specific uses. The MN Secretary of State's registered voter list has details about these restrictions as well as ordering information.
Read the privacy notice for voter registration applications to learn what data is kept private and why private data is collected, or the following question if you have concerns about your privacy.