I would suggest you to go through the following resources in order to get yourself acquainted with Bootstrap
Read this StackOverFlow entry of the question “What is bootstrap”.
Microsoft: DEV203x Introduction to Bootstrap :- This course is extremely beginner friendly, Christopher Harrison would walk you through all the basic elements of the framework like Page Layout, Forms etc.
Halen Stevens “Bootstrap: You’re Doing It Wrong” :- This blog post highlights some of the best practices that you should follow in order to produce beautiful websites.
Lastly, you can always access the Official Bootstrap documentation to know more about it’s features.