What a position is
Every lesson so far has kept your hand in one spot on the neck — first position. That spot has a name for a reason: it's not the only place the hand can sit. Stage 6 is about the rest of the fingerboard.
A position is where the hand sits, not which finger you use
A position is named by the note your 1st finger plays on each string when the hand is sitting in that spot. "1st position" — your only home so far — is the hand's base camp: 1st finger a whole step above the open string. "3rd position" doesn't mean "use your 3rd finger." It means the whole hand has moved, so that what used to be reachable only by the 3rd finger is now where the 1st finger lands.
The clearest way to see this: the same finger, in different positions, plays different notes.
Moving the whole hand this way — without changing which finger is "1st" — is called a shift. You'll learn how the arm actually does that in the next lesson. This one is just about knowing what a position is, before you learn to find one.
Half position: the one below home
There's one position below 1st, called half position. Instead of the 1st finger sitting a whole step above the open string, it drops to a half step above it — on the A string, 1st finger becomes B♭ instead of B.
Half position isn't for singing, unhurried lines — there's always time to shift properly for those. It earns its keep in fast passages that would otherwise force an awkward string change, and in flat/sharp-heavy keys (F major, B♭ major, E♭ major) that have no comfortable open-string anchor.
The roman numeral means this
Stage 3 taught you that a roman numeral over a note (III, IV...) can mean a string or a
position, and only context tells you which. Up to now that was trivia — your hand could
only ever be in first position, so a position-numeral had nothing to point you toward. From
here on, it points somewhere real: III over a note means the hand is sitting in 3rd
position when you play this, and you'll be able to check you're actually there (starting with
third-position, next movement).
Try it
Try
On the A string, play the open string, then place your 1st finger for a normal B (1st position). Now slide that same finger back a half step to B♭ (half position) and forward again. Feel that your hand barely moved — it's a small adjustment, not a shift. Say the position name out loud each time: "half position... first position."
The usual mistake
Hearing "3rd position" and reaching for your 3rd finger. A position number and a finger number are two completely different countings — one names where the hand is, the other names which finger is down. You'll use all four fingers in 3rd position, exactly as you do in 1st.