The simplest and slowest way when you need to use something from the system clipboard:

Copying: Enter visual mode (v) Highlight the text I want to copy then enter in command mode "+y which basically means "Use a register for following command (") make it the external clipboard register (+) and yank/copy (y)"

Pasting Move to where I want to paste then enter in command mode "+p to paste after the current position or "+P to paste before the current position

If I don't need to copy/paste stuff to applications outside of vim, then I can skip the "+ register setting part, and just use the default internal register.

Have you installed a clipboard, like wl-clipboard? you also have to set it up in neovim init.lau fila also with "clipboard=unamedplus" if you want it to be on your system clipboard similar to what you describe. The normal neovim setup is that the nvim clipboard is separate from the system one, but you can copy into it from neovim by using marks like "+yy etc. It's nice to have two separate if you can get used to it.

Edit: here is a guide. Disclaimer, i dont know if its good I only skimmed it https://hatchjs.com/neovim-copy-to-system-clipboard/

There are couple of factors that makes this a confusing topic.

Vim: On a high level, normally Vim (and Neovim) have their own clipboard system. Vim has multiple internal clipboards that can be used like variables and accessed with other commands. So its kind of sandboxed from your system. But you can explicitly use the commands to access the system clipboard. There is a configuration you can set to use the system clipboard by default.

Linux: Unlike Windows, in Linux we also have two kind of clipboards: the "system" clipboard as you know and the "primary" clipboard. This has nothing to do with Vim and is a feature on Linux systems itself. If you in example in your browser mark a text without copying, it is automatically copied into the "primary" clipboard. Then you should be able to access and paste it with middle mouse button in example. The system clipboard where you explicitly copy stuff is not affected by it.

You should read following documentation: 09.3 The clipboard - Neovim

Search for "copy from nvim to clipboard" you should get something right away.

I'd your highlighting text and copying that then it's your terminal not neovim

I sympathize. Using a neovim GUI should make things just work. Terminal and graphics never played well together, although you found nano to behave well.