Here. Imaginary numbers are "real" in the sense that we cannot find any way to explain them, but they work.
This is from Wikipedia:
Animaginary numberis a number withsquarethat isnegative. When anyreal numberis squared, the result is never negative. Imaginary numbers have the form biwhere bis a non-zero real number and iis theimaginary unit, defined such thati 2 = −1.
An imaginary number bican be added to a real number ato form acomplex numberof the form a+bi, where aand bare called, respectively, the "real part" and the "imaginary part" of the complex number. Imaginary numbers can therefore be thought of as complex numbers where the real part is zero, and vice versa. The name "imaginary number" was originally coined in the 17th century as a derogatory term as such numbers were regarded by some as fictitious or useless, but today they have essential, concrete applications in a variety of scientific, engineering, and related areas.
If that is too deep for you, try this link. Its on more of a gradeschool level.