How do top-up degrees work? And what are the equivalent to them in other countries?

Hello peeps:

I'm looking at different options for university and I was wondering how does a top-up degree work? I'm finishing my A level, and planning to go to neuroscience or something similar through a computer science route, as I have a strong background in computer science but a huge nerd of neuroscience and other things! The thing is I'm looking at several options and deciding on the best one... One option in particular is the top-up degree, which I could do an FP superior(like an traineeship in the UK or something similar, it is in Spain as I live there and worth 120 ECTS credit, equvialent to two years of study in bachelors I think). I struggle a bit with exams and looking at my options, including this more pratical approach. This approach might get me into where I want to be, as an example a masters in neuroscience or something similar, however I'm not too sure if it would get me there? So I ask, could a top degree work for me? Are there any equivalents things elsewhere that would get me to the masters level of where I want to go? How does the top degree work and what are the admission requirements?