There are three types of minor scales: the natural minor, the harmonic minor, and the melodic minor.
If you know your major scales, then you already know your natural minor scales. And if you know your natural minor scales, then you are one note away from knowing your harmonic scale. And the melodic scale is a combination of the natural minor and the harmonic minor. It is simple to know, but it takes practice to play it naturally, smooth, and easy!
Natural minor scales the sixth mode of any major scale. For example, play the C major scale beginning and ending on A, and you have played A natural minor. Play the A scale beginning and ending on F#, and you have played F# natural minor.
Harmonic minor scales are the natural minor scales with one note difference. The 7th note is raised a half step, and it sounds like music used to charm snakes. Just remember to play the lead note (the raised 7th of the natural minor scale) to the eighth note. For example, play A natural minor scale with a G# instead of G. Or play F# natural minor scale with F instead of E.
Melodic minor scales are played by raising the 6th and 7th notes of the natural minor scale a half step while ascending the scale and then playing the natural minor scale while descending the scale. It might help you to count the notes while ascending the natural minor scale and sharp the 6th and 7th notes.
This is the same as playing the major scale with the 3rd note flatted while ascending, and then descend the scale while playing the natural minor scale. For example, play C major scale with Eb (the third note flatted) while ascending, and then play C natural minor while descending.
Do you see it? Learning to play minor scales requires just a couple minor changes in notes.