The previous posters have the correct answers, but I'm going to answer anyway, just so it's perfectly clear.
1) What does "randomly selected" means here? It would be random if I roll a dice, I think...You pick who takes the damage, but the player who's taking the damage does not pick which character cards take the damage. Instead, randomly choose which of that player's character cards take the damage. Randomly choose for each point of damage. Rolling a die is a good way to randomize the selection.
2) I thought the team can always select who suffers the damage, so why "You select..."To make it clear that you still pick who gets damaged. If that parenthetical statement was not there, we suspected that some players would be confused about whether they got to pick who is taking the damage.
Also, to distinguish it from the Xenomorph Queen. The Xenomorph Queen damages a randomly selected player (you don't pick who takes the damage).
Thank you for asking. I hope this helps!