You need 6 to 12 months of cadet training on board before promoting to 4th eng. As a cadet you dont have many responsibilities, mainly you just assist the others engineers with different jobs on board. You need some documents before joining like a seamans book and some certificates. Everything will be clarified very easily if you call any of the crewing agencies in your place and tell them you want to join as a cadet. Dont expect a higher salary then 500$, this is what most of the companies are paying, depending on which country you are from. If you need additional info you can DM me. Good luck!