When I open nautilus does not open the left bar where it says computer and down markers such as music, documents, videos, downloads. I reinstalled nautilus from the synaptic package manager but nothing happened. What I can do to make that bar visible again?
Just press F9 when you open nautilus.
Another way to do this is
Click on 'view' then check the 'side pane' option.
Does pressing F9 re-show it? Or go up to the global menu, go to view -> sidebar -> show sidebar.
Just press F9 or if you like it the 'mouse' way, jut select 'Side Pane' from the 'View' menu.