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

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.

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.

It depends on where are you uploading your pictures. Irrespective of the place, you watermark must be small enough not to cover much of your photo. You can keep your watermark mostly around bottom corner.