The Nikon D750 focusing system is one of the trickiest to get the hang of if you are a true beginner. This video tutorial will help you learn when and how to use focus settings AFS, AFC or AFA.
The new Nikon D750 has improved focusing, improved ISO, improved low-light, improved moire, tilting screen, wifi, a built in flash. The Nikon is a great value and performance wise the D750 compares very well to competing Canon cameras, including the Canon 5D Mark III and Canon 6D in most ways.
Nikon D750 accessories can be found here.
Best prices on the Nikon D750 here and here.