✓ Accepted answer
The method used in the code :WorldToScreenPoint() returns a tuple in this case, essentially in the devforum code the developer wanted to store the tuple's return information in 2 variables having the first one as "underscore" ( _ ) because he/she doesn't want to really use it and marks it as irrelevant by naming it that way.
But essentially the method first returns a Vector3 for X and Y positions in the screen and a Z factor for depth and the second value returned from the method is just a bool that indicates if the point is within the screen, more information here:
https://developer.roblox.com/en-us/api-reference/function/Camera/WorldToScreenPoint