Need help in c++ concepts?

I need little help as I am new to competitive programming I know very little about some of concept. Please tell me about some functions inside bits/stdc++ or send me the link of any usefull website related to bits/stdc++ header file .

study from gfg everything is there on gfg
first understand some basic syntax of c++ then try to learn stl library such as vector
with practice you will understand everything
may this will help