Connect to Mac file sharing on iPad?

I've recently downloaded Infuse on my iPad and I would like to play some videos directly from a Mac. To be honest, I am not an expert of this file sharing stuff so I only reached the point when I have to use a username and password to log in but I have no idea what password or username should I use. I tried to share my downloads folder on my Mac but when I want to add a new user I can only choose from contacts. Basically there are administrators, me and everyone so I am confused how to solve this problem. Im sure you have much more knowledge about file sharing on Mac...