My camera came with 18-55 (wide angle) and 75-300 (telephoto) lens. I use the 75-300 all the time but rarely the 18-55. The wide angle lens is good for taking a photo of a large group of people, a landscape, etc. The 75-300 lens allows me to get good photos without being close to the subject. I use it a lot for taking photos of speakers at my Rotary club. I can stand at the back of the room and get a photo that looks like I was close to the speaker. If I could have just one lens it would be the 75-300.
EF was the mount for the new EOS system that replaced their FD mount in 1987.
EF-S lenses are specifically designed for the smaller APS-C sensor size, like on the Rebels. They're not compatible on full-frame cameras. These cameras have a white square on the mount's surface, along with the typical EF red dot that all EOS cameras have.