Sorry, no links handy. Spoiler- the server was a digital "dead drop" location for smuggling highly (extremely) classified data to the highest bidder. Data would be loaded into the server, then some brilliant "hacker" would "break in" to the server by cracking a password- like "password1" and "steal" the classified data. It was done that way to aid a plausible deniability defense should they get caught. Also, Colin Powell advised Hillary on how to set up the illegal server in a way to make it difficult to be detected by the law dogs.

The server was hidden in Hillary's basement, was illegal for her to even posses, and had laughable security. It contained classified, secret, top secret, and ultra-top secret S.A.P. (Special Access Program) data that Hillary did not have a security clearance for.