Hello and Welcome to LinuxQuestions,
You start at the beginning, which is most of the time the best point to start
First you get any doubts you might have out of the way by reading this: Linux is not Windows
and Linux FAQs for Newbies
Next you read some of the very good user manuals found on the internet, for example Rute's User Tutorial and Exposition
which will give you basic knowledge.
Last but not least you go over to DistroWatch
and look for some distros for newbies, for example Linux Mint, Ubuntu, CentOS, download as many as you like and start trying them out.
The best way to learn Linux is to get your hands dirty, so start installing and checking out stuff.