You have MAMP on Mac and you are trying to type "mysql" but it is not finding it.
1. Change to your user home directory with "cd ~"
2. Edit ".bash_profile" using the editor of your choice. (You won't see it if you list the directory contents - try "ls -a" if you want to see files normally hidden by the ls command)
3. Add the following line, which is the directory where the MySQL executable resides:
...that will attach the executable directory to your existing path and allow you to type "mysql" from anywhere.