Essentially Echo does have the ability to write to files (if you use >>) and the file has to be on the right side. The ~ means to create a file in your home directory and the .profile means that it will create that file (.profile) but it will be hidden from your view (in programs like the built in editor and file manager). If you run "ls -a" without the quotes then you can see files in a directory if they have a dot in front or not.

You cannot run programs from the SD cards because of the file system used on them. Also, if you want to make changes to a file (as opposed to dumping text into them) then you will need a text editor to do it. Vi and nano are possibilities. However, if you run the echo commands above properly the first time then an editor isn't needed... just make sure to run the right commands.