Ok, basically there are two different types of broad categories of lenses for Canon: L Lenses which are pro lenses, and just their regular lenses.
To hopefully get you to understand not all the regular lenses will work with all canon camera bodies (the higher end ones), while I believe all L lenses will work with all Canon bodies (or most of the higher end ones).
Now, onto what the lenses break down into further. There are a TON of lenses out there, there are:
Telephoto medium-long: Usually they have 50mm - 200mm focal length.
Super telephoto: 200mm+ focal length.
Wide Angle lenses: Lenses with focal lengths usually less than 40mm.
Ultra-wide angle lenses: Usually less around 15mm or less.
Macro Lenses: these let you see a subject with a 1:1 ratio or less (ie. a lens can have up to 1:5 ratio meaning you can see the subject 5x larger then they really are).
Tilt-shift: Not going to bother explaining these as you probably wont ever own one.
Anyways with that said each type of lens is different. The larger the aperture the better the backgroun blur and usually from 35mm to 200mm lenses will give the best results for portraits providing the best background blue (expecially the really long telephoto lenses), but the larger the aperture the better the background blur.
There are also another distinct category: zoom and prime. Primes usually offer better IQ, and you can achieve faster shutter speeds with larger apertures while with zooms they tend to be more versatile but they can be heavy (if we are talking about standard zooms, not comparing them to fixed apertures prime telephoto lenses). So if you want the best type of lens for a beginner I recommend not getting the kit lens with the T3i, rather just getting the body alone and save about $300, then I would look at a 50 1.4, or a sigma 30 1.4. Or if you don't mind the focal length and don't mind spending about another $500 I would recommend a 70-200 f/4L. It is a great lens, and yes it is more of an advanced lens but you will eventually grow into photography and want better lenses so why not start out with a good lens?
Eventually you will understand what is good and what isn't but don't be fooled just cause Canon has their L series. The lenses are very expensive or they can become very expensive. I would recommend just getting a Sigma for staters.