Brief explanation of the concepts of shell and sub-shell before working with SQLite in earnest. A system shell is a command-line interpreter: it takes commands in the form of text typed on a line after the so-called prompt (which tells you where you are) and passes it on to the operating system. An example for a system shell is "bash". But when you open SQLite, you also open a shell where only SQL and SQLite commands are understood. Going back and forth between system shell and SQLite shell is important when you import or export data for further processing, like queries.