cout<<"Enter your first name and last name separated by space:";
cin.ignore(20, ' ');
getline (cin, name);
cout <<ch<< " "<< name;
This may not be a perfect explanation, but here goes.
cin.get(ch); This will get the first and only one character. Even if you type more than one character from the keyboard.
cin.ignore(20, ' '); This will remove the next 20 characters or up to a space which ever comes first from the input buffer. This i more often written as cin.ignore(2000, '\n '); or std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); // <--- Requires heder file <limits>.
getline (cin, name); This is the best way to enter a string especially one with a space in the string. This will retrieve everything from the input buffer including the new line character. The new line character will be discarded when stored in a string variable.
Line 10 just shows you what each variable contains.