Open a procedure. On the green starter block, change "No additional trigger" to "Player joins the world". Unfortunately there is no way that I know of to make this be for the first time, but if you're trying to make them get an advancement or be teleported to a dimension, then this will work. If you need more help, let me know what it is you're trying to do :)
make a global variable called something like "playerjoinedworld" (make it a number and GLOBAL_WORLD) and when "player joins world" set the global variable to (Playerjoinedworld + 1). and if you want to see if the variable is true in any procedure, do (IF [playerjoinedworld = 1] Then [write code here])
Open a procedure. On the green starter block, change "No additional trigger" to "Player joins the world". Unfortunately there is no way that I know of to make this be for the first time, but if you're trying to make them get an advancement or be teleported to a dimension, then this will work. If you need more help, let me know what it is you're trying to do :)
make a global variable called something like "playerjoinedworld" (make it a number and GLOBAL_WORLD) and when "player joins world" set the global variable to (Playerjoinedworld + 1). and if you want to see if the variable is true in any procedure, do (IF [playerjoinedworld = 1] Then [write code here])
You can do it only in the first time. Let me know if you still got this proble to help you.