Open D chord pattern with capo at the 6th fret would sound as an Ab.

C would be a Gb.

And G would be a Db.

If you start out with BIAB in the key of G, then entered the chords as D, C and G in the right bars, after that just go to the keysignature dropdown box and change the key signature to Db to have it sound the same key as your guitar is playing when the Capo is on the 6th fret.

And keep studying, music is not something that can be learned overnight. Take it a little at a time. Consider paying a music teacher, too.

BTW -- I don't know how I missed your question for so long, I don't think the post was visible at my end until just now...

--Mac