Research internships at universities and funding I'm going to graduate next summer from my bachelors. Before pursuing a masters program, I'd like to get to know research groups at different universities. Some universities seem to offer some kind of internship programs but I couldn't find any clear information.

How does it generally work? Can one do 6 months or a year of research at another university between bachelors and masters? Does it cost money and where can one find funding?
It all depends. You can join a summer REU program, where you can get funding. You can go on various websites of professor who may be advertising positions, and contact them. Keep in mind this, sometimes, the particular opportunity that you are looking for may not exist (in your case, 6 months/1 year research at a university, as a non-student). That means that you will have to contact professors (even if that means contacting tens of them), and ask them if they would be willing to consider bringing you on for that long. Obviously, you will need to offer them something, like strong computing skill (which will really distinguish you). As I looked at your profile, it seems like you do have a strong computing skill, and so I would advertise that. Another great option (which I did in my previous life), was join the IT department of a specific academic department, and slowly find the opportunity to network with faculty and let them know regarding your skills. Slowly, you will have the opportunity to possibly engage in research and strengthen your graduate school application. In life, often times you have to make your own opportunity. I wish you the best in your future endeavours.