I am totally new to the world of computer OS installation. I have used Windows softwares like MS Office etc. but never really formatted any PC or installed any OS. I dared to install VMWare and run Ubuntu on it. However, I find it very slow. I am curious to explore Ubuntu fully and need step by step guidance on how can I install Ubuntu on my PC without deleting the Windows OS that I am using now. I want my PC to have both the OS.I also want to know whether I can buy a new hard disk and dedicate it fully for Ubuntu. Kindly help.
Here's a great resource: https://help.ubuntu.com/community/WindowsDualBoot
Hopefully that will help you out. The steps may vary slightly depending on the Ubuntu version you're installing. And be sure to back up all data you don't want to lose before you install Ubuntu.
I suggest a safer alternative just to "have a go" is Wubi.
This has practically zero chance of nuking your Windows install and will let you try out Ubuntu just about as well as installing it natively. It runs on bare metal (that is to say, its not inside a VM) but disk access is a little slower since it has to go through another layer (it translates disk accesses to a file on the Windows filesystem).
No repartitioning required, which is probably the most dangerous bit for a new multi-OS user.
I would say go with Wubi for now and when/if you get a new HD, set it up with dual-boot in mind from the start.
I've found the best guide to recommend to new installers of Ubuntu is one that documents the process well and also has screen shots to give you an idea of what to expect on the screen as you install the OS.
The guide here gives you a very good overview of different types of dual boot installations and is very comprehensive.
It hasn't been updated since 10.10 but the Ubuntu installer has not changed that much since then anyway.
Good Luck with your install!!