To get the distance from the enemy to the player use this:
distance(enemy.x,enemy.y,player.x,player.y)
if you want to know if this distance is less than 100 pixels use:
system compare two values: distance(enemy.x,enemy.y,player.x,player.y) < 100
the distance is measured in every direction so 100 is like a circle around player.x,player.y with a radius of 100px