In any lens, elements are the specific lens pieces used and how are they arranged to obtain a particular feature, the arrangement is the group. Lenses pieces are usually arranged in groups. In lens, say if it is a zoom lens, it will have more number of elements and groups, where as for a prime lens, it will have less number of groups and elements. 

Usually it is termed as the more number of groups and elements, the better the quality but it is not always true. Lens quality also depends on the type of glass, design mechanism, manufacturing process of the lens. So for a particular focal length, a prime lens would be better than the zoom lens.

Prime lenses usually perform better than zoom lenses.

The only thing you need to do so is a DSLR.

It also depends on  DSLR as to which type of AF technology  it uses or what are the diffrent types of focus points that the camera has.

And just automatically or manually focus your subject and you are ready to go.

By this you should be ok to focus on.

1. Shooting with 50mm lens can let you shoot at aperture as wide as 1.8 but a 18-55mm will allow you to shoot only at 5.0 aperture 
2. This difference itself is a huge deal. This means you can have the advantage of having faster shutter . Imagine shooting handheld at 1/15s with aperture f5.0 and then at 1/125s with aperture f1.8. This can be significant in low light conditions.

If it is your first DSLR, then no.If you have a lens kit already there is no need for that. If the price between a body, and body + kit lens is negligible, then it’s ok to get one with the lens, if you’re just starting out and have no other lenses.Some kit lenses are paired quite well with their camera bodies, and do perform decently.Experiment with the kit lens, discover shortcomings, if any, and use it to help decide what to purchase next as you learn and progress.

In the wedding photography you can mostly click candid photos, because the expression we want to capture comes unexpectedly. Portrait photos are the best clicks because in the wedding there are lots people people's gathered, so it is very difficult to get required space. Thank you 🙏💕. 

There are basically three fundamentals that you should follow for photography. Those are

1. Shutter Speed
2. Aperture
3. ISO / Film Speed

You can find a nice article on this fundamentals over here

But before that, you need to practice on Program Auto or Auto Mode (Creative Mode on Canon) for clicking in perfect composition. When I bought my camera, the sales guy suggested me to start with the only composition, rest you can master later. 

Here are some photo composition tips by Steve McCurry - The famous photographer