How to continuosly check for a condition to be met?

I need a code to continuously check if a certain condition has been met. I tried using if statements, but I noticed they only check for it when the script is run, or they are called in a function. I tried using a while loop, but, That was catastrophic. It almost crashed studio. I don't even know if a for loop would work because when I typed for #script.Parent.Detector1:GetTouchingParts() == 3 do, the hashtag was underlined red. I am looking for a way to run the function only once, and only when the certain condition is met. Here is the part I need help with:

if script.Parent.Detector1:GetTouchingParts() == 3 then -- My dumb attempt at using an if statement ? --
	print("touching three parts")
end

Help is greatly appreciated. Thanks!