The scientific keys
Trig (sin, cos, tan and their inverses), square roots and powers, natural and base-10 logs, ex and 10x, π, e, factorials and Ans. A function key types its name and an open bracket, so sin, 3, 0, = works out sin(30); the bracket is closed for you. Everything can be typed as well: sqrt(2), 2^10, 5!.
Degrees or radians
Deg is the default, as on a school calculator, so sin(30) is 0.5. Pick Rad for radians, where sin(π/6) is 0.5. The inverse keys answer in whichever is chosen: asin(0.5) is 30 in degrees and 0.523598775598 in radians. Angles on the axes come out clean: sin(180) and cos(90) are 0, not a leftover like 6e-17.
Powers, roots and logs
2^10 is 1024, and whole-number powers of fractions stay exact: (2/3)^3 is 8/27. For roots other than square, raise to a fraction: 27^(1/3) is 3. log is base 10 and ln base e; type log(8, 2) for base 2, which is 3. Factorials are exact too, but an answer longer than 15 digits is shown in powers of ten, so 20! reads 2.43290200818e18. Roots, logs and trig give decimals to 12 significant figures.
Questions
Can it do nCr and nPr?
Yes, typed: ncr(5, 2) is 10, the ways to choose 2 from 5, and npr(5, 2) is 20, the ordered ways. They have no keys of their own.
Can it solve equations or draw graphs?
No; that is the Algebra Calculator, which solves for x, shows the steps and draws graphs.
Why does tan(90) say Undefined?
In degrees, tan(90) has no value: the tangent runs off to infinity at 90°, so the calculator says so instead of showing a huge number like 16331239353195370. log(0) and the square root of a negative number are refused the same way, with the reason.