Do i have to go through the BIOS settings and all that in a pre-built PC?

It should come with the right BIOS settings. If it's a laptop, connect the charger and boot it up. (i.e., Don't do the first boot on battery.)

Most new computers will take you through a first-boot setup, where you enter your name, and make some other initial selections. So allow plenty of time to do that. You should also be prepared to leave it running, connected to the Internet, so it can install any pending security updates.

Usually not, but there are a couple of things that might require you to mess with BIOS settings:
1. If you want to allow your PC to boot up from a bootable CD, a USB Flash Drive, or a USB External Hard Disk, you might need to enable this functionality in BIOS, and re-configure the order in which the BIOS checks for bootable storage devices.
2. If the computer came with a 2tB or smaller hard disk, the BIOS might be configured to use MBR partitioning only. If you want to upgrade to a hard disk larger than 2tB, you will have to go into the BIOS and tell it to allow GUID Partition Table (GPT) hard disk drives. If this isn't configured properly in BIOS, you will not be able to install Windows into a partition larger than 2tB, and would not be able to utilize the disk with the full native size of it's larger-than-2tB capacity in one partition. If this is unfamiliar to you, it is rather complicated; try to have someone who is a Windows SysAdmin or at least a "power user", explain and walk you through how to do this. You can brick the operating system on a hard disk by fooling around with partitioning if you don't know what you are doing or ar using the wrong software.

I would because I like having my settings just so, but you don't have to.

Buying a prebuilt store bought pc is a plug and play thing you won't have to do a thing except turn it on

No, everything should be configured to automatically work unless specifically stated otherwise. If you do have to, something has gone wrong. I would often see this with system being delivered by courier - the usual culprit being a detached drive during transit although sometimes a little worse.

Even on a new build, you should be able to get away with minimal interaction with BIOS (actually called UEFI not BIOS - consider it depreciated) if any at all during the boot process.

You need to install Windows, so you will have to obtain a copy of windows on a USB flash stick. Your hard drive is essentially empty and requires a operating system to run.

Provided they installed an operating system and set the proper device to boot from, you shouldn't need to mess around in the BIOS at all.

if this is a new pc then the BIOS is owned by windows now because of the changes and addition of the UEFI. the BIOS is almost DEAD.