Already have partition

I took my PC to Best Buy to have them install Zorin. It took them 10 days to tell me that they didn't install it because they don't support it. They did create a partition. So, where do I go from here?

Well, if it was me, I'd install Zorin on that partition.

What is the make and model of the PC? Is there a reason, given the PC, that they believe Zorin will not work on it? OR is it only that Best Buy does not want to accept any liability in installing Zorin OS?

I have an HP Pavilion. It has 1 Terabyte hard drive. The partition was split evenly. I think it's more that they don't want to accept the liability.

When you say that you'd install Zorin on that partition, which would be B:, how does that work? I followed the instructions to download balenaEtcher and created a boot drive on a USB.

Do I restart the computer and open the Boot Device Menu? And will it then ask which drive I want to install Zorin?

You would select boot from USB from your computer boot sequence.
Then you can choose Try or Install Zorin.

In installing Zorin, you will go through some prompts, such as location and language... Then arrive at a screen that says "Install Zorin Alongside..." If you read down that page, you will see an option for "Something Else."
Choose "Sometehing Else" and the installer will open a Partition Manager. From this, you can select that partition that you already have set aside.
Ensure that you set a Mount Point (You can choose just / as the mount point) and ext4 journaling.

Okay, I got it until "Ensure that you set a Mount Point . . . "

What's a mount point and ext4 journaling?

And I watched a video where the user was setting up a certain amount of space for /dev/sda, /dev/sda1 ext4 /, and free space. Not sure how much space I'm supposed to give to these devices.

Also, after I install Zorin, when I turn my computer on, will it give me the option of starting under Zorin or Windows? Which I assume it would.

Sorry if I'm belaboring every point, but I'm new at this.

The mount point is the directory to install within. If one is not set, this will halt the installation. I remind others to ensure they select one because in the gparted screen, it can be easy to miss.
ext4, fat, fat32 - all of these are Formatting Options. Here is more detailed information on ext4 journaling FS:

How much space is entirely up to you and depends on how you use the computer and what you tend to save, but generally on the forum, we seem to say a bare minimum of 60 gigs.

If the installation goes properly and smoothly, then at boot you should have the option of starting under Zorin OS or Windows.
If it does not, we can repair grub.

No apologies are necessary when you are ensuring that you have everything in order.