Find a common denominator.
Example: ¹⁄₂ + ²⁄₃
¹⁄₂(³⁄₃) + ²⁄₃(²⁄₂) (Let’s make it six)
³⁄₆ + ⁴⁄₆ = ⁷⁄₆ (Add now)
Here is a geometrical explanation for it. Imagine you have two pizzas. One pizza is bigger than the other. Both pizzas are cut into 8 equal slices. Is one of slice from the big pizza the same as one slice from the little pizza? Nope. The slice from the little pizza is smaller than the one from the big pizza. This is why you need a common denominator. One slice of the bigger pizza is not equal to one slice of the smaller pizza.
I hope this helps! Don’t hesitate to message me if you have any questions!