You have neglected to mention the OS you are using.
One way is to use the sqlite3 command in your terminal.
sqlite3 db/development.sqlite3
However, for things like inspecting your rows, you would be better using a rails console.
rails c
> User.all # Where user is your model.
NOTE: Do not change your DB schema directly through sqlite3, something you may be used to if you come from a different web stack background. This is because the next time you run the migrations, the state will be different to what rails expects.