A:
If you wish to connect the drive to both a PC and Mac, then you will need to choose your filesystem wisely, or ensure you have the appropriate software on both sides so you can read/write to the filesystem that you choose. Setting the drive up to go between is not terribly difficult, but if you are not comfortable reformatting drives then you may encounter difficulties.
If you format the drive with the Mac OS Extended filesystem (or some variation of the Mac filesystems) then you can basically only use the drive with your Mac. You'll need to install special software on your PC to access the Mac filesystem.
If you format the drive with NTFS, then you'll be all set on the PC/Windows side. The Mac can read that filesystem, but you may need additional software on your Mac to write to the drive.
Various options are available via some simple web searches. Good luck.