Singer Model 500 help please

It took us ages to attempt to thread it and now we can’t get it to knit. It will do the first row, then undoes it when we take the carriage back. We’re totally new at this type of knitting and have no idea at all. Youtube failed me as well, so can anyone explain to me, please, how you get the machine to knit? Is there an online help somewhere? I have looked, but can’t find it. Many thanks.