For example, if a note in the original score is written as C, it would be played as E♭ in concert key.
There are a few different ways to transpose music up a minor third. One way is to use a transposition chart, which shows you which notes correspond to each other when transposing up a minor third. Another way is to use a capo on the viola, which will raise the pitch of all the strings by a minor third.
If you are transposing viola music for a performance, it is important to make sure that you are transposing the notes correctly. Otherwise, the viola part will not sound in tune with the rest of the orchestra.