Wow. Completely unhelpful advice from your tutor there. You probably need a better tutor. But, Canon does have an equivalent to CLS. I just wouldn't call it a must-have feature on a flash.

Main factors to consider:

1. Budget. Obviously, you only have so much money to spend. So, how much you can afford is going to limit your choices, just as budget probably limited your camera and lens choices.

2. Features. How you plan to use the flash will determine what features you want. This can greatly affect the price tag. There are two main patterns of usage:

   1. On-Camera. This is where you use a battery powered speedlight (hotshoe flash) attached to the camera's flash hotshoe. It's most common to use this type of arrangement for run'n'gun event or social shooting, when you need to be light and portable, and bouncing is the most typical technique. If this is your usage scenario, a more expensive flash with Canon's eTTL II capability, and 360º swivel will be very nice to have.

   2. Off-Camera. This is where you are using any type of flash/strobe (battery powered, mains powered, studio strobe (monoblock or pack & heads), bare bulb, or speedlight) mounted off the camera, typically on a light stand. This is most typically used for studio-style lighting setups. You can go anywhere from super-cheap (manual speedlight) to astronomically expensive (TTL/HSS capable studio strobe) here.

      Tripping the flash remotely from the camera may require sync cables, or radio triggers. With this type of flash, manual power control is mandatory, and how the flash can be remotely triggered/controlled is more important. eTTL may be less useful, as automated power control for speed isn't of the essence in a studio setting, but it can give you more control over remote lights (if they're speedlights). Power, however, is going to be the main concern, here. Think of power on the flash like maximum aperture on a lens. The more you have, the more situations you can handle, but the bigger and more expensive the gear gets.

Starting out with a Canon dRebel, for a first flash, I'd recommend getting an eTTL/HSS capable speedlight. This way, you have a light that you can use both on and off-camera. Your budget should probably be at least US$200 (if you're in the US), although you can spend less if you're willing to go with cheaper Chinese brands and their possible issues. You don't have to get the most expensive, latest and greatest Canon flashes (600EX-RTII or 430EXIII-RT), you can look for their predecessors used (600EX-RT, 580EXII, 580EX, 430EXII, etc.) Or at third party flashes from Phottix, Godox, Sigma, Metz, Yongnuo, etc. Just be sure they're for the Canon hotshoe system, and 3rd party makers will also make Nikon, Pentax, Four-thirds, Fuji X, and Sony flashes.

If it were me starting out all over again, this week :), I'd probably go for a Godox Ving V860II if I had the budget, a TT685 if I didn't, and be looking at the Godox X1 system, because of the expansion/integrated triggering system. But I shoot off-camera and multiple systems. You're not me. So, do some research to see what's going to fit you, your budget, and how/what you shoot. (And if you're not the OP, and found this answer by googling; check the date, and realize specific model advice on Chinese flashes passes its sell by date really fast, as in weeks/months).

Flashhavoc is a great resource for researching what's out there right now. And the POTN board's lighting forum is full of folks with experience in this arena.

See also:

• What features should one look for when selecting a flash?
• What does an expensive flash unit buy over a cheap one?
• Are Yongnuo flashes interchangeable between dslr's or are they brand specific?
• How can I get started with a first flash gun?