Examining a game with a friend.

How do I examine a game with a friend where we can both draw arrows and lines and see what one another is showing?

use a study, that might work

Look at the Tony Rotella video
lichess.org/blog/V0KrLSkAAMo3hsi4/study-chess-the-lichess-way

Yeah, use a study. They are incredible.

I'm not seeing how I can set up endgame positions and everything else. (subtracting/adding pieces etc.) Am I missing something?

See at 10:27 in the video for the board editor
See Thibault explanations in my link:
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Each chapter has its own move tree and starting position. There are many ways to create a chapter:

INIT: start from the initial position.
EDIT: Setup any position on a board editor.
GAME: Load a lichess game replay.
FEN: Paste a position.
PGN: Paste a game replay. Variations and comments are preserved.
d27t3nufpewl0w.cloudfront.net/lichess/426d1b9080f6ccd30bdad76bdb2c93e66b704580_chapter-create.png
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@kifaru Thank you very much.