There are lots of advanced techniques for identifying things. If you have a pink potion you can throw it at a monster, and based on the monster's reaction you might now know what pink potions are. Most of this stuff would be hard to learn on your own though.
You can also identify rings by dropping them down wells—different rings fall down (or don't fall down) the wells in different ways—and identify wands by writing on the ground with them. Definitely hard to pick up any of that on your own, though.
I think you mean "sinks" instead of "wells" (there's at least one behavior in NetHack that's inspired by the name of the sink, and they were reputedly included in the game so that NetHack would contain "everything, including the kitchen sink").
Good catch, my mistake. Thanks.
You get potions, scrolls, weapons etc but have no clue what they are until you use them (some scrolls will help you identify what other things are in advance). Nothing about them will give you any clue (scrolls have names like "AFEWA AWEBRPO", potions are just colours etc.) To survive you need to use them though. You need to drink, but the potion might be one of weakness, poison, blindness, confusion etc. You need to eat regularly, and food is scarce, but it also might poison you. A ring of slow digestion is helpful there, but until you use an identify scroll on a ring you won't know what it is. It could end up being a ring of attract monster, for example.