What does it mean by a kit?

Like when they say a Nikon D3100 Kit. Does it mean that it comes with lens etc?

A "kit" from the manufacturer only means it comes with a cheap lens. The kit has nothing else that you do not get with the body alone. In other words, if you buy the body alone, you still get everything you need, including the battery, strap, CDs, battery charger, owners manual, warranty. The "kit" only adds a cheap lens.

Now, some places will add to the kit with other VERY cheap add ons, but they have nothing to do with the manufacturer kit.

Most people starting out need the kit lens. Photographers who already have lenses only need to buy the body.

Be VERY careful where you buy the camera. There are MANY scammers out there. If buying on line, use B-H or Adorama or Porters or Ritz.