Writing user scripts requires knowledge of JavaScript. The tutorials on the GreaseSpot Wiki should give you a running start on JavaScript both in general and as it relates to user scripts. Inspecting others' scripts can be helpful. You may be interested in Greasy Fork feltöltött szkriptekre vonatkozó szabályzata and Szkript önleíró kulcsok, amiket beolvas a Greasy Fork. If you want help developing your script, feel free to kérdezzen a fórumon.
To post on Greasy Fork, you will need to create an account. From your felhasználói oldal, follow the link to új szkript feltöltése.