Input Fields

The main difference between Global and Local variables is the scope - that is, the range of code where the variable retains its value.

When a variable is declared as Local, its scope is limited to the function - or the part of the code - where the variable were declared.

Consider this example:

test() ;call a test function
Print "MyLocal outside the function: " + MyLocal ;prints 0 because MyLocal scope is only inside the function

function test()
local MyLocal = 5
Print "MyLocal inside the function: " + MyLocal ;prints 5
end function

So, when you need a local variable, just for calculations an the like, then use Local.

Instead, when you need a variable to be accessed in every point of your code - that is, in every function and every place of your code - then use Global declaration.

A variable can be declared Global only in the main part of your code - that is, you can't declare a Global variable inside a function.

Time for another example:

Global MyGlobal$ = "mintybreath"
;call a test function
print MyGlobal; prints "mintybreath"
test()
print MyGlobal ;prints "Hello mintybreath"

function test()
MyGlobal = "Hello " + MyGlobal ;updates the global variable
end function

To summarize: use Global when you need a global scope for your variable. Example: score, player name, speed, etc.

Use Local when you need to compute some value which is only temporary needed.

Don't forget also Costants. A Costant does not change its value, and it's also global by default - that is, you can access it in every piece of your code, exactly like a global variable. But the Costant value can't be changed:
Const PI# = 3.14
print "PI outside the function = " + PI; prints 3.14
test() ;call our lovely test function

;uncomment the next line to generate a compile error: a constant value can't be changed
;pi = pi + 1 ;generates a compile error.

function test()
print "PI inside the function = " + PI ;prints 3.14
end function

Hope this helps,
Sergio.