There are three loops.
Two of them are next to each other.
The outer, or express, loop the trains go counter-clockwise and stop only at MK and TTC.
The inner, or local/resort, loop goes clockwise and, starting at the TTC, will go to Poly, GF, MK, Cont and back to TTC.
The Epcot loop will go from the TTC to Epcot, looping arounf the inner section of Future World before stopping at the Epcot station, and will then return to the TTC.
The most they will have is four trains on any loop, and they run continuously. On busy days it is not unlikely to have one train ready to pull into a station as another is leaving.