Big majority of computer users used to open files and folders by double click on mouse. But, there is option to change mouse behavior, so You can open files and folders by single mouse click. There are many pros and cons about this behavior, all depends of a user and his/her habits, ways of computer using.
In example, it's good for faster opening files and folders, but it's not good for previewing files in Nautilus, because You must click on a file (select it), so You can preview it. This can slow all the operation, because You can not click on a file (this will open the file), but You need to select it.
I am going to show You how to change this behavior and You decide whether You'll change it or not.
Open Nautilus and head for Edit->Preferences and choose Behavior tab. In the first section, Behavior, You can change mouse click behavior, by choosing Single click to open items.
I was long-time KDE user and I loved very much this feature in KDE. But, Unity differs from KDE and here the option isn't that usefull like in KDE.
As You can see, in the same tab is other options. There is also option for adding DELETE action in Nautilus context menu. Look for it in Trash section, at the end of the tab. Just mark the box before Include a Delete command that bypasses Trash.
This is very usefull (for me), because I don't like moving files to Trash and then click to Empty Trash. Boring to me... By including the command in Nautilus context menu, You will be able to bypass Trash. My advide to You is not to uncheck previous option, Ask before emptying the Trash or deleting files. It's a good safety measure.