It is confusing at first, but they are multiple ways to play any chord.
A G major chord is just G B and D. So you could play that on 3 strings. But usually that’s not what happens. Different ways to play a chord are called voicings. One common way to play a G major chord is the four finger G 320033 (the 3rd fret on the E string, 2nd on the A string, open D string, open G string, 3rd fret on the B and high E ) which is G B D G D G, so GBD with a extra D an octave up, and two extra Gs. It makes it a bit fuller and richer. Another common way is the three finger G 320003 (same but leaving the B string open). That’s G B D G B G, so it’s still a G chord but has two Bs and only one D. The three finger version, played with the middle, ring and pinky fingers, is popular in songs that move G to C because it makes an easier transition.
Most of the time for Tony’s challenges I’ll use what he suggests. Some times I fall back to the version I use the most. Occasionally he’ll call out that you really want a particular fingering to make the movement easier. But feel free to use what you are most comfortable with.
As time goes on you’ll likely end up learning different voicings of many chords and choose them for reasons of sound, ease of transition, or leaving a convenient finger free to embellish the chord. But starting out, use whatever is most comfortable.
If you search for “ways to play g chord on guitar”, you’ll get a ton of answers with titles like “learn 8 ways to play a g major,” “5 ways to play a g chord,” and “12 different ways to play an open g chord”. Those will be there when you’re ready. Until then just have fun learning one of the common versions.