Each member of the scale has a name based on its relationship to the first note of the scale. They are commonly referred to by 3 types of names:
Scale Degrees. These are numbers that always have a caret over the top.
Solfege (e.g. Do, Re). These are commonly used for sight-singing.
Functional Names (e.g. tonic, supertonic). These names will also refer to the chords we will build above these scale degrees.
The natural minor scale, as compared to the major scale, lowers scale degrees 3, 6, and 7:
The C major scale is: C D E F G A B C (or 1 2 3 4 5 6 7 1)
The C natural minor scale is: C D Eb F G Ab Bb C (or 1 2 b3 4 5 b6 b7 1)
When we're in minor, we refer to those 3 altered notes differently as b3, b6, or b7 (unless they are raised as in melodic minor). The same goes for solfege and functional names (e.g. we say Me instead of Mi, or Subtonic instead of Leading Tone).
See the melodic minor scale below:
1 / Do: Tonic
2 / Re: Supertonic
(b)3 / Me: (Flat) Mediant
4 / Fa: Subdominant
5 / Sol: Dominant
(b)6 / Le: (Flat) Submediant
b7 / Te: Subtonic
7 / Ti: Leading Tone (when 7 is raised in minor)
Note: This varies a lot between sources. In Musition (and elsewhere), scale degrees are sometimes just 1234567 regardless of major or minor. In this scheme, 7 refers to both B and Bb in the scale above. In functional names, for the mediant and submediant, sometimes you'll see "flat" before the name, sometimes not. In Musition, you won't. That said, Subtonic is always reserved for the lowered form of 7 in the natural minor and leading tone is always reserved for the raised form. Solfege, conversely, is fairly consistent. What you see above is what most teachers/sources use for "moveable do" solfege.