A capo is a clamp. It shortens the sounding length of the strings. Every open shape you already know now sounds higher.
Capo on fret 2 with a G shape does not sound as G. It sounds as A. You still think G, C, and D with your hand. The room hears A, D, and E.
That is the whole trick. The capo is a hardware transpose that keeps your favourite shapes. ChordJoy's key chip is a software transpose that changes the letters instead.
Each fret is one semitone. Capo 1 raises a G shape to G#. Capo 3 raises it to Bb. You do not need a chart of all twelve on day one. Count from the written key.
Ukulele players use capos less often because the scale is already short, but the same math applies. Piano has no capo. On piano you just play new letters.
If a friend sings Amazing Grace higher than the written G, capo up and keep the G-C-D grip. Or move the on-page key and learn new grips.
Decide which view you want. If you capo and still want the pad to show G, C, and D, leave the page in G major. Your ear will hear a higher key than the screen.
If you want the screen to match the room, move the page toward A major or D major and take the capo off. Now the letters match the pitch.
Silent Night and Ode to Joy are calm pages for this experiment. Play once with a capo and once with the key chip. Notice which one lets you look at the neck less.
If you need to go down from the written key, a capo cannot help. Capos only raise. Use the key chip toward C major or F major, or tune down.
A thick capo on a cheap neck can pull strings sharp. If the pad sounds sweeter than your guitar, check the clamp before you blame the chart.
Three-chord Song in G with capo 2 is a clean drill. Four bars, three shapes, a known rise. Then open When the Saints Go Marching In and do the same thing on a real page.
The chord player online will not put a plastic clamp on your neck. It will change letters. Use both tools. They solve the same pitch problem from two sides.