Is it better to open a new tab or window?
A tab is more or less same as a window. A window can contain several tabs and all session data and cookies are shared across all tabs and open window. It's better to open a lot of tabs than opening several windows because too many window becomes too cluttered to handle.
How do I open a new tab without leaving a page?
If you want to open a new tab with no website open, you can either click the "new tab" button in the browser's tab bar, go to the "File" menu and click "New Tab," or type the letter "t" while holding down the Control key.