You need to format your new hard drive through Disk Utility before re-installing OS.
Step 1. Before you start
a. Insert your Bootable Mac OS Mojave USB Install Drive into the USB jack of your computer.
Step 2. Turning on Computer
a. Hold down: Command + Option + R, while holding this down, hit the power button to turn your Mac on.
b. Continue to do this until you see the Apple Icon appear.
Step 3. Set up Wi-Fi Connection
a. Select your Wi-Fi network and enter in password if your Wi-Fi is password protected.
Step 4. Format your Hard Drive.
a. Once the computer has completed updating and processing the changes you made, you will see a menu appear.
b. BEFORE doing anything else, select “Disk Utility”.
c. A new pop-up will appear once Disk Utility is open, Select your Hard Drive.
d. Click “erase”. Erasing the Hard Drive is Formatting the Hard Drive.
e. Name your Hard Drive.
f. Click “erase” again.
g. If a window appears asking if you want to erase all information on the hard drive, continue. This should be a brand new hard drive, with no risk of losing information.
Now your disc is formatted.