See the attached sketch.
The devices 1, 2 and 3 can be masters* or slaves.
The terminators are connected between the A and B wires at the two ends of the RS485 buss.
Where the buss length is short (less than 2 metres at a guess), it will work with only one terminator, but for best results terminate at both ends as I have shown.
JimB
* Usually there is only one master, however...
I once built a system which had two masters and three slaves on an RS485 network.
Only one of the masters could be active at any one time, due to what was driving the masters.
As far as I know it is still working 15+ years later.