What is the intuition behind the Lorentz factor from Special Relativity

Time Dilation = $1/\sqrt{ 1-v^2/c^2}$ but why? How do you get to that conclusion? I know you use Pythagoras'theorem and my current understand goes like this:

$$vt^2+ct^2=cT^2$$

then you take the square root of $Ct^2$ and from there I think you divide by $c$ to get the time dilation but I'm not sure. And if this is correct what steps do you take to get to the formula used now