How do you know if a square root of something is rational or irrational? like i know it can be represented by a fraction or a ratio of two integers but like how would √17 be irrational? explain

The square root of a whole number will be rational if the whole number is a perfect square (i.e 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144 etc) and irrational otherwise.

Rational number is a number that can be described as m/n 

so a fraction can be a rational number, 0.8=4/5 
Irrational numbers can't be written as a fraction 

The part about the number having to be a perfect square is still correct, if it's not a prefect square than it will just keep going(a decimal that never ends) 

for example the square root of 0.64 is 0.8 
and the square root of 10 is 3.162277... 
as you can see the 0.64 one ends and is rational, whereas the 10 one just keeps going and is irrational.