All scientific and graphing calculators have the ability to find square roots. Usually, the key involved has a square-root symbol: √. The particulars can be found in the manual for your calculator. (Sometimes, a shift operation is required to access that key.)
If you only have a 4-function calculator, you can still get close, but it takes several steps. The basic method is to divide the original number by a guess at its square root, then average that result with the guess to make a new guess. Continue until you have the accuracy you desire.
For example, √17 ≈ 4. Dividing 17 by 4 gives 4.25, and the average of that with 4 is 4.125. Dividing 17 by 4.125 gives 4.121212... and the average of that with 4.125 is 4.12310606... This is good to 5 significant digits. (4.1231).
_____
If you're concerned with roots of index other than 2, you can use a similar method to the above, but it gets more complicated for higher roots. For example, the next guess for a cube root of n is (2/3)x + (1/3)n/x², where x is the present guess.
_____
For calculators with a yˣ key, the value of x can be the reciprocal of the root index. For a 5th root, you would use x=1/5. That is ...
[tex]\displaystyle\sqrt[n]{x}=x^{\frac{1}{n}}[/tex]
_____
You can always use logarithms to find roots. The log of the root is the log of the original number divided by the root index. That is
[tex]\displaystyle\log{\left(\sqrt[n]{x}\right)}=\frac{\log{(x)}}{n}[/tex]
