I'm still trying to understand what a "set up" is. For the most part, that's just a preferencial thing right? Like some people might rather have aftermarket strings, pickups, bridges, etc. to change the playability or the tone of their instrument. Right?
I'm mostly familiar with how a factory P bass sounds based off the videos that I've watched on YouTube with people demonstrating it. Fender channel, Andertons, PMTVUK, Tyler Spicer are a few that I've watched.
Might be more information than you're asking for right now, but a setup is just a procedure of ensuring an instrument is in proper playing shape. A setup should make the instrument feel and sound better (to you).
A simple bass/guitar setup checks Relief (setting the appropriate bow in the neck via adjusting the truss rod to allow the strings to vibrate freely), Action (setting the strings the proper height off the frets via saddles at the bridge and, less than ideally, the nut; setting the string height to match the curvature of the fretboard), Pickup Height (distance between the strings and the pickups, usually adjusted with a screwdriver), and Intonation (adjusting saddle position at the bridge to lengthen/shorten the string so fretted notes play at the proper pitches).
These are all things most players can (learn to) do with a good tuner, an accurate ruler, a screwdriver, a couple of properly sized hex wrenches, and the right information (a good place to start is with the manufacturer's suggested measurements, which can usually be found on their site or in guitar maintenance resources, and then those values can be tweaked to match an individual player's preferences ... For a P-Bass, here is Fender's guide:
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There are other processes in a complete setup like fret-filing and neck shimming, but those are a little more involved -- sort of bordering on repair -- and hopefully won't be something you'd need to do to a newly purchased bass.
As a new player, having this done by a professional is probably the way to go, especially if (as mentioned above) they're willing to give you a rundown of your instrument and an explanation of what they're doing and why.
Over time, however, learning to do your own setups can help keep your instrument in proper shape, saving money in setups and (hopefully) avoiding more costly repairs.
As someone previously posted, TB has an entire section dedicated to instrument setup. If you have questions, there's no doubt someone there will be able to help answer them.