Ninjutsu: Ninjutsu are normal jutsu done with raw chakra(and requires no element) i.e molding of raw chakra.
Chakra: Chakra is a kind of energy drawn from the spiritual aspect of the body.
Elemental ninjutsu: Elemental ninjutsu is the molding of chakra with one of the five elements.
Differences between ninjutsu and elemental ninjutsu: Ninjutsu requires only raw chakra while elemental requires one of the five elements. Also Ninjutsu is weak to elemental ninjutsu because of the elements added to the elemental ninjutsu.
Taijutsu: Taijutsu is in relation with Ninjutsu cause most taijutsu skills requires chakra except the gates
kenjutsu: Kenjutsu is in relation ninjutsu cause some ninjutsu attacks can be done with/through weapons and also chakra can be placed on weapons
Genjutsu: Genjutsu is also related cause it is done with chakra. Genjutsu can also be describe as using chakra to interupt the opponents chakra flow causing a type of illusion, therefore i can say genjutsu is a type of ninjutsu done on the opponents mind.