a. Use Disk Utility (installed by default), this application not only allows you to partition but also allows you manage the volumes (like mounting and unmounting, benchmarking, bootable, and checking and repairing). I find it much prettier, more hardy*, and generally a more enjoyable experience than gparted.
To partition: Click on the drive you wish to partition on the left (you can see the description) format the drive (see figure) and then click in the Volumes area (which will say "free space") to add partitions.
Note: I haven't added a screenshot of the actual partition screen, as I don't fancy formatting any of my drives, if someone has one please edit it in!

b. The partitions will be "available" (seen on the left hand side of nautilus), but won't be mounted by default - necessary if it's music libraries and stuff, to do this use pysdm
- Storage Device Manager.
Find the partition(s) you wish to mount on start up (locate it's name from Disk Utility e.g. sdb1), click on assistant. Uncheck "Mount file system in read only mode" and keep "The file system is mounted at boot time" checked.

Click Mount, Apply then Close, and restart your system (part b. is taken from here).