I have a one page HTML built site, I am moving to Wordpress and want to know will I lose my Google rankings? Thanks
If you move it correctly, not changing anything other than swapping out a static page for a CMS, it shouldn't change anything in search engine rankings.
However, you will have to make sure the site is as accessible as it was previously, the URL is exactly the same (or properly redirected), etc. A CMS can have a lot of features, some of which must be configured, others maybe turned off. For example, you'll want to keep your site speed the same or better, so if you're using a theme, you'll want to make sure it's lightweight. You will also want to manage the plugins properly, and delete any unnecessary ones from the backend. (These are just some of the things to think about. There are many books written on the topic of optimizing self-hosted WordPress.)
Search engines don't care which CMS or website builder you use, but the accessibility and performance of the site - which do have an impact on rankings - are up to you.