Why we will use using namespace?

Answer 1

And without namespace
Std::cout>>"ghebjsjsn";
Std::cin>>

Answer 2

So you dont have to write std every time you use cin or cout or anyother code line. Its pretty much saying that the program will be accessing entities whose name is part of namespace called std.

Answer 3

With using namespace std your code will look like this
Cout<<"ftgsjhssisbsjisb";
Cin>>ghhsbs;