I want to introduce an NPC, can I do that?

Yes of course. When we are writing we need people for our characters to meet and talk to, and we can't use player characters all of the time. Just include your new character in your post.

If you are going to use this character loads of times then you can add him/her to the Crew Roster. This will show their profile to everyone else and allow other people to use your NPC.

Please don't try and add every random person to the Crew Roster though, especially if you're never going to mention them again!