XF 1.3 Botton in the post

I want to insert button in the post, i have search through all the resources and posts but i didn't find any easy way of doing it. Most of the add-on are complicated. i just want to insert simple button for a url.
Please help
Thanks for assistance
Thanks Brogan for your quick response, can you please help me how to create a custom BB code and how i need to use it. i have very limited knowledge related to these things.

Thanks for your assistance