New Ubuntu user, no string under cursor error in cpp file and arrow keys type ABCD instead of moving cursor

Hi, I'm brand new first day using Linux through Virtual Box and trying to follow a Youtube tutorial to make a C++ Hello World file. I opened the cpp file in a terminal using "ls" then the "vi first.cpp" commands and now I'm stuck with an error E348: No string under cursor when I try to start the header file with a #. The # won't type. Also I'm finding it frustrating that the arrows will type letters and not move the cursor, so is there a way to fix that?
I'm using Ubuntu.