Very VERY beginner here and I'm taking a big by bite outta this project.
I bought a arduino nano, little audio board (and a audio amplifier that I have NO idea how to all connect) and I'm reading documentation on how to connect the audio board
And it says that the Vin is the power in, but I'm learning how to use jewels and they have a ground, positive and a Vin as well, but I connect the 5V from the nano to the positive on the jewel and not the Vin.
Read the documentation very, very carefully, and carefully follow the instructions or you may end up destroying modules.
Many modules, and to my knowledge all Arduinos, have a voltage regulator on board, in which case the voltage of the power source may be freely chosen within stated limits. Many of those modules and the Arduinos also provide a fixed output voltage for powering other circuits, within limits.
For many modules, you are required to provide 5V or 3.3V. Use a fixed 5V or 3.3V output on an Arduino to power for those modules.
Finally, beware that 3.3V modules can also be destroyed by connecting their input/output pins to a 5V Arduino. For that purpose you will need "level shifters".
When you talk about any modules, include a link to the exact one you are talking about. The nano is easy enough, but "jewels"? I won't even try googling it.
As for the Adafruit module, they are pretty good about telling you what pins to hook up, what voltage is needed, and if any level shifting is needed.
As for pos/neg/Vin- Those terms are self explanatory, but only tell you part of what is needed. You still need to know what voltage it requires, and even if you require both inputs. It would be best to stick with modules that spell it out for you until you get a better grasp on electronics. Buying stuff off ebay generally leaves you on your own to figure out without frying it.
The nano is easy enough, but "jewels"? I won't even try googling it.
They are 7 Neopixel LEDs on a small circular board.
but I'm learning how to use jewels and they have a ground, positive and a Vin as well, but I connect the 5V from the nano to the positive on the jewel and not the Vin.
Those things require 5V and so should not be connected to Vin which is always greater than 5V. In total they will take about 420mA so will normally need an external 5V supply. If you never put them on full you can get away with powering them off the 5V output from the board but watch for overheating on the regulators of your nano. They contain a series resistor already so you just need a large capacitor across the supply, something like a 47uF.