Ninjutsu: It allows shinobi to acomplish feats otherwise unable to do. It uses hand seals and chakra to be effective.
Elemental Ninjutsu: It works on manipulating your chakra to produce effects of the 5 natural elements;Water,Fire,Wind,Earth,lightning they are used like a game of Rock,Paper,Siccors*Only Anolagy i could think of* as in one is stronger than they other but none of them is the best and 2 of them together could augment a ninjutsu(example fire and wind) fire consumes wind thus making it stronger.
Diffrence: there is many other type of ninjutsu that produce diffrent effects. But elemental ninjutsu bases itself only of the five elements.
Chakra and its relation to ninjutsu: You could consider the fuel to ninjutus you need chakra to be able to control and use ninjutsu. You shape and mold chakra to be able to use ninjutsu. You also need chakra control to be able to produce the affects wanted to little chakra or too much chakra results in non-propure use of a technique.
Raiton:its one of the 5 elemental ninjutsu. It allows the user to create lightning by increasing vibrations in the users chakra frecuency.
BLUE SKY:its created from the rays of the sun and the glass efect of the atmospher creating blue light waves. And what does this have to do with training? XD