Most clarinets play in the key of Bb, although A-clarinets are quite common too.
When you want to play along with non-transposing instruments, something has to happen with your notes...
If you have access to the notes as written in C (as for piano, flute or violin) it's an easy trick:
For a clarinet in A more or less same story, only select transposition C to A.
Now what if you have a part written for tenor saxophone and want to use ith with your A clarinet ?
Say, if you have a piece of music written in D major (two sharps) for the violins with a Bb-clarinet part coming with 4 sharps, and you want to play that piece with your A-clarinet?
It might be useful to use fingering-symbols like L or R for clarinet parts.
To make sure that a clarinet sounds (more or less) like a clarinet use the instrument dialog