As with past and future tenses, imperatives based on the aorist stem (often with an -σ- in them) are for single events, while those based on the present stem are for continuous, continual, repeating, or habitual events.
So you might say Χρησιμοποιήστε το κουτάλι! if you are talking to a guest to indicate that they should use a spoon now (at this meal), and Χρηστιμοποιείτε το κουτάλι! for example when you are talking to someone who has come from a country without spoons and you are teaching them that they should (in general, always, again and again) use the spoon.
The sound of /s/ implies "once, not continually" χρησιμοποιήστε (use once), αγοράστε (buy once), τρέξτε! (run now!), χορέψτε (dance) etc.
To soften the imperative and make it sound a bit more polite or casual, we add Nα:
Να χρησιμοποιείτε το κουτάλι (continually)
Να χρησιμοποιήσετε το κουτάλι (once) Notice that I've put one more ε there. It happens when we use the Να.
I wouldn't think that the possessive is necessary in English, but I am not a native speaker. Why would it have to be 'your' spoon? If you replace 'spoon' with another object maybe as in 'Use a/the chair to reach high shelves'?
In Greek, either the possessive or the article make sense depending on the situation.