For using a magnetic cartridge to play music on any regular Garrard turntable or changer (assuming you are going for entry level magnetic carts) the following criteria have to be met:
1) your turntable headshell (both detachable and non detachable types) has to support either half inch mount or p-mount type carts (older Garrards have a single-screw cartridge mount, for which an adapter can be used with half inch mount possibilities (good example is the Garrard SP25 MK1 and MK2 headshell)
2) your tone arm should be able to track at between 1g and 3g (VTF) or your choice of magnetic cart may be limited to those that track at 4g+ like the Shure M3D
3) the tonearm should be wired for stereo (most Garrard tonearms are, except for the very early ones from the pure-mono era)
4) you should have an amplifier with a Magnetic phonostage (MM) or use an external phonostage