33/77 as a percentage is 42.86%. This value tells you how much of a whole 33 parts out of 77 represent when you think of it in terms of 100.
The fraction 33/77 can be simplified by dividing both numbers by 11, giving 3/7. Whether you look at 33/77 or its reduced form 3/7, the percentage stays the same.
Knowing the percentage helps you compare this fraction to other numbers easily. For example, if you score 42.86% on a test, you got about three‑sevenths of the total points.