I am only curious and want to contribute to this site in a meaningful way.
That right there is the key phrase. The reason new accounts aren't allowed to make sales threads is, there's a fair amount of folks who never attempt to make conversation or contribute to the forum- they make an account & immediately set up a sales thread, often skipping the requirements for having one here becuase they're copy/pasting the same sales post into multiple forums. Sometimes it's a scam, sometimes it's just a reseller casting a wide net- either way, it's bad for us becuase these are not people who'll stick around after a sale, so if anything goes wrong? Good luck finding them again.
The fact that you're posting this puts you instantly ahead of the kind of account that tends to get banned, so don't worry too much. My recommendation would be- don't make a sales thread yet, but do browse the forum. Not just the marketplace, but overall. It'll help you get a feel for what kind of folks are around here. This is doubly important if you're intending to make a sales thread, becuase it'll give you an idea of what would be worth attempting to sell here. For example: there's not a huge amount of discourse on the pre-NES era here, so trying to offload a Bally Astrocade would be a terrible idea- you'd save that for a more vintage skewing forum. We're also slower moving than some other places, so it's not necessarily the best choice for a quick sale.
Take your time, learn a bit about us, & when you're feeling ready for that sales thread I doubt anyone will be bothered by it.