How do you add meteor to your previously made website?

I have made a website with html, css, and javascript, also using customized bootstrap files. I would like to add accounts to the site so I decided the best way would be to use meteor. I need to convert the website to meteor form now, and I have done a lot of research to try and figure out what the form exactly is. So far I have only figured out that you do not need to use html tags, and the best way to route things is with iron router. I understand I am far from getting this to work, but if anyone could create a list or just describe the steps I need to take to get ready to actually start coding with meteor, that would be fantastic. An example of the problems I am encountering is I have no idea how to import my own css files. Thanks for any help!