These questions are not clear enough. These questions typically provide little information as to solve the question. These may provide little to no script, no error or output information, have no general idea where an issue is occurring, little information in general. These questions may rely on the person answering to have to sift through several lines of code to get an idea where an error is occurring.
Some suggestions against having your question closed as Non-Descriptive:
Have multiple print() calls in your script. Print out variables and messages indicating where the script currently is in its execution.
local gui = script.Parent
local function SayHello()
print("inside the function")
gui.TextLabel.Text = "Hello"
end
print("calling SayHello")
SayHelo()
Provide any errors that appear in the output window. Give information as to what your intended result is, provide us with code if needed (but only what should be necessary), provide steps to reproduce the issue and screenshots if possible, as well as the type of script you're testing, how you're testing, and where the script is located.