You may want to try this guide: https://medium.com/@dun.chwong/the-ultimate-guide-ubuntu-18-...

I also had to resort to looking at guides on Medium.com for installing CUDA, as the install is not as straightforward as it looks. Alternatively, you can search on DuckDuckGo (for privacy reasons) with this as the query: "NVIDIA" AND "CUDA" AND "install" site:medium.com