I'm a noob . . . what's STF?
Special Task Force missions.
There are 3 Borg STFs split into 2 segments each. Space and Ground.
They can be accessed through the PvE queues or set up as a private instance.
They are 5 man group missions, that require extensive team work compared to all other missions in the game and are generally a lot harder to beat, some of them can be outright failed or at least produce head injuries (banging you head on your desk because of frustration if you end up with idiots playing. Idiots can be "veterans", too).
There is one old school STF you can access in the Gamma orionis sector called Terradome which can be accessed like any other mission but also requires a team to beat. It features the Undine.