Registering new applications with Asterisk

I am in the process of developing a new application for Asterisk. I will have a .C file at the end of the development that I would like to merge with the existing Asterisk system and make my new function work in my dialplan. How do I go about doing this?

Further, I wanted to see the existing registered applications with Asterisk. When I write “show applications” from my CLI terminal, I get a response saying “No such command show applications …” What could be the problem?

Thanks in advance

You can try with:
core show applications

That worked. Thanks.
But how do I add a new application ?

You look at an existing application, and it should be obvious.

I did couple of small applications - just the way david55 explained. Got one, made my changes - and I have new application.
For really small ones - I used existing application file, for bigger one - I created my application file.