Tap the frets and notes you already know. You get the chords that contain them, with shapes you can play and hear. Charts follow the left/right-handed setting at the top of the page (left-handed by default).
Frets you know
Tap a fret to mark a note on that string. Tap the circle above the nut for an open string, again for a muted ×, and again to clear it.
Notes you know
Matching chords
Root note
A fret you picked
Strings run low E to high e