Unlike a physical calculator with a limited number of buttons, or a graphic interface app with a limited space on the screen, Hypatia has no problems offering a large number of operators.
Some of them offer primary functions, including what you'd expect from a scientific calculator but also some that you would not that easily find elsewhere (like normal distributed random numbers), others just offer shortcuts in calculations you could, if more complicated, do without them (like the six percentage operators).
Do not worry, that all these operators exist does not mean you have to know them all by heart.
But if you still miss any operators that you might find useful, you can create them yourself (see chapter "User Defined Elements", page "User Defined Operators").
1-Argument Operators: Arithmetic 1-Argument Operators, Trigonometric Operators, "IS" Operators, Measurement Unit Conversion Operators, Large Number Units.
2-Argument Operators: Arithmetic 2-Argument Operators, Percentage Operators, Rounding and Limiting Operators, Random Number Operators, Compare Operators, 2-Argument Unit Conversion Operator.
n-Argument Operators: Statistical Operators, The ITEM Operator, The n-Argument Delimiter.
Constants: PI, TAU (PI times 2), E (Euler's number), PHI (the "golden ratio").
Pseudo Constants: RAND, DUP, I, ISLOOP, TIME.
Pseudo Operators: WHISK, DONE.