Will WordPress affect an existing website in my hosting folder?

Hi there everybody…I’m new to this and know just enough to be dangerous, so please forgive the rudimentary questions…

I have a very basic website set up in a hosting account, and want to evolve it now to a nice and capable WordPress website…

So my question is this: If I install WordPress to the folder and start working with it, will it eradicate the existing site sitter there? How do I open the WordPress site and CMS offline and work with it until the site looks like I want it to be online?

Thanks so much…
sv