Welcome to the guide! I’ll get straight into things. There are two simple ways to tell someone. Not talking, or having “no mic” in your Steam name. Other than that, there’s not really an amazing way to tell people. You can “signal” to other players easily in-game.
If you’re stuck outside of a room people may assume you’re an SCP and attempt to speak via the error message when you try opening the room, such as “2 clicks for yes, 1 for no”. Aside from that, if you’re not in a hurry, you can signal yes and no by either jumping twice (if the person tells you to), or simply nodding/shaking your head no.
If you want someone to follow you or go somewhere, then you can waste a bullet or two shooting in the general direction, or moving back in forth towards the desired direction.
This can be used for telling teammates to open doors, lockers, follow you, etc. You can use the radio with V if you have one. As if that’ll be useful.