I've been using neovim as my terminal multiplexer for a couple years now. I can use all the same key commands for yanking and pasting buffers from a file buffer to a terminal buffer.
Do you have any particular issue? Does it give you a real tty?
If I need to copy, I'll use the terminal normal mode (ctrl-w N) and visually highlight text and copy it to the + register. Then I can paste the contents in another application. The only issue I've encountered is that some text that's not supposed to be wrapped has line breaks added at the screen width. In that case, I'll paste the text into another vim buffer first and remove the line breaks using gJ. then copy and paste it into another application.
For copying text from another application back into vim, I'll just highlight it with the mouse and paste it into vim using ctrl-w "*