No prob, buddy.
Let's start from the beginning, shall we?
Iaido- The art of drawing the sword from the sheath and cutting the opponent in one motion. Also includes grappling with sword and sheath. Some styles may actually include sword fighting techniques, although I'm not too sure about that.
Kenjutsu- The actual sword fighting art you imagine samurai to have used. There are many schools, and all of them have seperate techniques. Sadly, kenjutsu is being phased out in favor of kendo in most places. Kenjutsu is really quite lethal, includes stand up sowrd fighting, grappling with and without a sword. A really well balanced art.
Kendo- The sporting form of kenjutsu, when you see two people smacking the heck out of each other with bamboo swords whilst wearing armor. It's a good art, but I personally feel that it leaves out some of the more significant techniques of kenjutsu, namely the grappling and ground-fighting.
Nitto-Ryu- An offshoot of Kendo and Kenjutsu, a subsection, really; but I thought it deserved mention. Nitto-ryu is the art of fighting with two swords at once, pioneered by Miyamoto Musahi and Tsukehara Bokuden.