simple motion sensor

but the comelier says nothing about a problem.

There are two types of errors: syntax and logic. If the compiler doesn't throw an error that means you have no syntax errora, but it doesn't mean there are no logic errors.

how are the variable names to be?

[/quote]
Descriptive

an how i can test a code on arduino without the loop... i don't get it
Incidentally, I still have no arduino

Write a blank loop.

I want to be safe the with the program
before I buy one

There is no danger in programming the Arduino