Transfer to US uni after 3 years in Europe?

Hi everyone, I recently got my Bachelor's degree in Europe, and I was thinking of transferring to the US for an extra year. I know this is doable as I have heard of other students that did it previously, but I don't know what this is called exactly (is it called just transfer? lol). Also if anyone has done this, do you have any stories/tips about how you applied and how the year was compared to Europe?