Even more basic here.

Everything that people are teaching here is based on the diatonic scale.

The anchor points on the scale at the 2 ends are Octaves (8 notes) A physicist could tell you why, but the important thing is that we tend to hear octaves as the same note. Men & women easily sing parallel octaves apart without thinking about it. It's the ultimate in a 'consonant' sound.

Much of our western music breaks the distances between the 2 ends of the octave into 7 intervals of uneven 'size' or distance. This is what a tin whistle does. A piano & fretted instruments use semi-tones or half steps to break that octave into 12 intervals.

The scale everyone has been using a reference is commonly known as a major scale. With a - to indicate the distance between the notes, the interval distances are:
1--2--3-4--5--6--7-8

There are whole tones between all notes except the 3-4 and 7-8. You can put your finger on the neck of the guitar, begin at any location, skip a fret to play the whole tones & go to the adjacent for the half tones; you've got a major scale (at least until you run out of neck). On a piano those black keys are like the frets. Start at any point, skip over or play the note according to the pattern & you can play a major scale in any key. Again, C is all natural so when you count the keys you see that 3-4 & 7-8 have no black key between them, automatically giving you the half tone.

You can take that some repeating pattern of whole & half tones & end up with scales that are called by differnent modes.

1--2--3-4--5--6--7-1a--2a--3a-4a--5a--6a--7a-1b

A scale that starts on the 2 & goes to 2a is what's usually called a Dorian minor & is very common in folk music. 6-6a is a natural minor. (Harmonic minors are for a more advanced class) Going with no accidentals in a key signature, the natural minor goes A-A, major C-C, Dorian D-D. If you have a tin whistle play a scale that begins & ends with 1 hole uncovered & you've got Dorain. Begin & end with one hole covered, etc. is a natural minor.

I used the numbers above for illustration, but in real usage the scale gets renumbered. When talking scales the key note is usually denoted 1 as one regardless of the mode. Thus a natural minor scale:
1--2-3--4--5-6--7--8
Has the half tones between 2-3 & 5-6.

This is why just looking at the number of accidentals in the key signature does not really tell you the key. One sharp is G major, but it's E minor. Determining which is which is also for a more advanced lesson :-)