Natural MinorThe Natural Minor scale has the following pattern of half-steps (H) and whole-steps (W):

W-H-W-W-H-W-W

Here is a Natural Minor scale starting on F:

Harmonic MinorThe Harmonic Minor scale has the following pattern of half-steps, whole-steps and one augmented second (A2):

W-H-W-W-H-A2-H

Here is a Harmonic Minor scale starting on F:

Melodic MinorThe Melodic Minor scale is different because when we go up the scale we use one pattern and when we go down the scale we use another.

The ascending pattern is: W-H-W-W-W-W-H

The descending pattern is the Natural Minor Scale: W-H-W-W-H-W-W

Here are the ascending and descending patterns for the Melodic Minor scale starting on F: