Trigonometric functions are defined on the angles and for every angle if you apply any trigonometric function to it, it will generate a unique value. For example, tan of 45 degrees is equal to 1.
Inverse trigonometric functions are the reverse of above defined trigonometric functions where you apply the inverse function on any number and you can get the corresponding angle for which the trigonometric value is defined for that particular angle. For example, tan inverse of 1 is 45 degrees, since tan of 45 degrees is 1.
Trigonometric function operate on angles and give you values whereas inverse trigonometric function act on values and give you angles as the output.