When you joined the forum, you promised to read and abide by the rules. The How To Use... is right next to the Rules.
Click on the Forums tab on the main tool bar. Then click on
Instructions for how to use Downloads should be at or near TOS in the sticky area.
However... Downloads was adapted from the XenForo Resources module, so it was not originally designed as a Files storage system. There are some things that I would change if I could. One is that you cannot look at what is available unless you have also been granted the rights to download something. So all that I can offer is that if you want to say what it is that you are actually looking for, I will try to tell you whether or not it is there.