Actually you are not noobish because Fort wasn't widely played and back in the days of 2.86 was mostly played by RA players when the could get the admin to put it on.
First of all I would like to say Fort was in a state of flux, changes were made, planned and such so what I describe here may not be exactly what others remembered.
A series of control points, marked by flags are placed in the map. There are some variables to decide how many but I believe it was mostly based on map size and number of players. The idea was to capture the control points much like you do TAS until you have them all. You respawn at a control point that your team has, in waves simular to EAS I believe, so as your team gains or loses control points your options increase or decrease until finally you can't.
When I last played it was non-linear so major chaos can occur. Also the matches can take a long time to finish such as an hour in Trenches.