How to enter music for transposed instruments

I'm new to MS, so I have some start-up problems.
I've a piece of music in C-major, i.e. all instruments are written as c-major even the transposed instruments like Clarinets, Horns, Trumpets etc.
If I set up a score for this piece I get all untransposed instruments in C-major, Clarinets and Trumpets in D-major, Horn in F in G-major etc.
1) If I now want to enter the music for these instruments in C-major which I have as Input, what do I have to do? 2) Later, when I'm finished entering the music, I want to show the transposed music in the score and parts. What are the steps for this?