how can i install os on a second hard drive

Yes, you can.

Yes. Either start up the computer with the Command and R keys held down and install an OS, or use a program such as the Disk Utility, Carbon Copy Cloner, or SuperDuper to clone an existing OS installation to it.

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Search Bing or Google for cloning Mac OS X or even the forum, you should find that it has been asked every day almost and cloning, installing etc and links to Macupdate.com for "clone" - I switched back over to Carbon Copy as it makes putting a recovery partition on every day that much easier / it lets you exclude files and folders (only do so with user media and data you don't need on boot drive)

Depending on model and if you have 2012 or earlier, then your 2nd drive should probably be an SSD, and here that has been in practice for 6 yrs makes a nice even huge difference in performance.

http://nyacomputing.com/how-to-create-a-bootable-clone-of-your-mac-hard-drive/

I would say it is 99% normal common and a must. Maybe a couple - a bootable copy of your working system, no need to "install" it. One that you can use to restore from in addition to TimeMachine.

Not knowing what model Mac Pro whether it is 6,1 Late 2013 or something older and what its options are.

http://liondiskmaker.com/

Lets you create your own clean install Mavericks installer (use flash, hdd, any bootable volume)

http://www.bombich.com/

Carbon Copy Cloner vs. Super Duper-Which is better? ( 1 2 3 4 5)

http://forums.macrumors.com/forumdisplay.php?f=1