Your classical guitar has nylon strings, which can take WEEKS to settle in (because they take a while to stretch to their full length). But once nylon strings settle in, the guitar will stay in tune for months.
An electric guitar takes less time to tune (you only have to stretch and retune a few times), and you can get it to stay in tune in a matter of minutes. But you usually have to retune an electric guitar every couple days at least.
Some people stretch the stings before they even put them on the guitar, but I like to put them on and then stretch each one (by pulling it up and away from the fretboard).
Good luck!