It seems like you are kinda confused at the moment on lot of stuff. Autocompletion with nvim-cmp and the related projects can be a bit messy but it is manageable when you take a look at the doc. Here is what I can advice to first familiarize yourself with the ecosystem:

• Use Kickstart to setup your first configuration
  • Alternative: use a distro such as LazyVim, LunarVim...
• Take a look at some articles, videos and stuff - there are a lot of content available that will explain you how to start a nvim config from scratch and to get basic configuration working properly.
• Take your time, read the doc, read other people config (look dotfiles on github) and enjoy the journey, it will be a long one !