honeymoon in Spain

Hey everyone! Planning my honeymoon to Spain for next year and I am at a loss trying to figure out some documentation things. We are US citizens and will be going to Spain. Passports are good to go but we will be going to Andorra for part of the trip. I cannot figure out if I need a visa or anything else to enter Andorra, and more importantly return to Spain after. Trying to understand the Schengen visa process is very confusing and I would love any advice.

Thanks so much for the help! 🙂