There are three types of gimbals (and one or two "sub types"):
Full size "U shape" with dual posts, the lens sits on a platform in between them. This type has the highest weight ratings to support the heaviest lenses, provides both tilt axis and panning axis, replaces any other head on the tripod making it largely "long lens only" (unless another head is swapped with it). Manfrotto 393 is an example.
Full size "J shape" gimbal that replaces any other head on a tripod. There are "bottom mount" and "side mount" sub-types. The "bottom mount" (foot of lens' tripod mounting ring is positioned at 6 o'clock). This type has a high weight rating to be able to accommodates most lenses. The "side mount" type requires the lens' tripod mounting ring be positioned at 9 o'clock or 3 o'clock, has slightly lower weight rating, so might not be ideal for the heaviest lenses (400/2.8, 600/4, 800mm). Both sub-types offer a lot of adjustment to be able to most precisely set equilibrium with various lens & camera combos. Both sub-types completely replace any other head on the tripod and provide both panning axis and tilt axis control, but make the tripod "long lens only" while installed. Some are convertible from bottom to side mount. I think the Wimberley head was the original full-size gimbal head years ago, but there are many brands of them now to choose among.
Gimbal adapters are used in conjunction with a heavy duty ballhead that has an Arca-compatible quick release platform. The adapter is simply installed when wanted, so the ballhead stays in place and the tripod can quickly be reconfigured for "standard" (non-gimbal) use. All gimbal adapters are "side mount" and provide tilt axis movements, while the ballhead's horizontal axis is used for the panning motions. Gimbal adapters have somewhat lower weight capacity... The Wimberley Sidekick that I use was recommended for up to 500mm f/4 lenses (tho I've seen folks using them with heavier lenses without any problem). Some other brands may not have as high capacity. Induro and Jobu make adapters, too... There may be others. When using an adapter, the ballhead's carrying capacity also needs to be taken into consideration (heavy duty are typically more than enough).
To be practical to use on a gimbal, any lens needs to have a tripod mounting ring (to allow switching the camera between landscape and portrait orientation).
You also need to install a somewhat oversize Arca-compatible lens plate on the tripod ring's "foot". That's needed to mount the camera and lens on the gimbal. It allows the camera & lens to be slid slightly forward and backward to achieve equilibrium (when that's set ideally, the lens & camera won't tip even if the gimbal's tilt axis locking knob is left "loose"... though I still keep a hand on the camera "just in case").
You need to be aware that lenses that ARE NOT internal zooming/internal focusing... such as your 200-500mm... are not 100% ideal on gimbals. They work very well (I use both an adapter and a full size with a Canon 100-400mm at times)... but IZ/IF lenses work even better. The reason is that the lens changing length will upset the equilibrium on the gimbal. Depending upon the weight of the particular lens and camera, it might be only a little, or it can be a lot if there. But gimbals simply work best with internal zooming/focusing lenses, which... once set up... stay very nicely balanced regardless how their focus and/or zoom are set. When set up, a gimbal allows a very light touch to smoothly move a large lens/camera combo around, tracking subject movement.
An accessory I find very useful with gimbal mounts is a leveling platform. This goes between the head and the tripod leg set, to provide a means of quickly setting the head to level. It is possible to do so by adjusting the tripod's leg lengths, but that's slower and "fussier" (and maybe a little risk, should you forget to re-tighten a leg lock). I use Gitzo Series 3 Systematic tripods with Gitzo leveling platforms. Those replace any center column. But I've seen other brands that are usable with center columns, if you happen to use one.
Here's a pretty comprehensive list of available gimbals:
http://www.carolinawildphoto.com/gimbal_list.htm