There are 3 ways to fire an off camera flash.
1. The worse way, (in my opinion), is as a "commander" type operation. That means the pop up flash on the camera causes the remote flash unit to fire. This is a system used by both Canon and Nikon. The pop up flash outputs a very low flash so, in theory, it has little effect on the photo, but I simply do not like the principle of it and it is very distance limited.
2. Infrared optical trigger / slave. As you have a Canon, this could be an option for you. An infrared trigger mounts into the camera hot shoe and when you press the shutter, the trigger sends an infrared signal to the flash unit and causes it to fire. It works well, but does have a serious drawback. The trigger and receiving flash must be in line of sight with each other. This can really be a problem at times trying to mount the flash so it can "see" the trigger on the camera. Canon is, thankfully, phasing this out.
3. Radio Trigger. This is by far the best method. Canon now has a radio trigger and certain flash units that work with it, (the 600 EX flash being one of them). Like the optical trigger, it mounts into the hot shoe of the camera, but it sends a RADIO signal to the flash. When you activate the shutter, the radio signal fires the flash. This setup works wonderfully and can fire the flash(s) even if they are around a corner and at quite long distances from the camera. The Canon set up is NOT cheap, and I also think it does not function with the T6 camera, but I am not sure of that.
There is a way, however, to have a radio trigger set up no matter what camera or flash you may have. There are MANY third party manufacturers who can provide what you need. "Pocketwizard" is one of the best, but more expensive than many others. (Keep in mind, with photography equipment, you often get what you pay for, so even though you can certainly find much cheaper alternatives, you may end up sooner or later paying the money for a better set up). Anyway, with a third party set up, the radio trigger mounts into the camera hot shoe and a separate receiver is then placed wherever you want it. The flash then mounts into this radio receiver, (which has a hot shoe on the top of it). The trigger unit on the camera sends the signal to the radio receiver and it activates the hot shoe and fires the flash. Most of the better units will still support ETTL automatic flash exposure. You need to learn how to set flash power manually also though for the best control of your lighting situation.
I'm not sure what you mean by "multiple exposures"? The flashes will fire for every exposure unless you turn the radio trigger off and / or adjust the flash power. By the way, in most cases, you can adjust the flash output power directly at the radio trigger unit, you do not have to be going over to adjust the individual flash unit(s).
Finally, I have given you the basics. YOU are going to have to do lots of indepth research to find what works with your set up and at your price point.
You are also going to need light stands with flash / cold shoe mount adapters and AT LEAST two flash units, three or more would be even better.