My hard drive crashed
can I download my operating system from somewhere since my hard drive had to be replaced
Google “download Windows 10” or whatever your OS is.
OEM factory installed systems have licenses injected into the system board. As long as you install the correct version, it will work.
This looks like an older laptop, you may have to install Windows with the Windows Install Disc. You can attempt to create bootable media for Windows 7, Windows 8, or Windows 10 to install to the new drive. However, you need to make sure that the hardware inside it supports the requirements of Windows. If they do you are ok to install, if not you will need to re-install Windows XP that came with the laptop.
Or if you have a backup of the drive you had in the machine before it died, you can use Windows Restore to restore the image you had from the other one to the new drive.