I observed that Following main Questions which are **frequently asked** usually tagged with [tag:apt] or [tag:software-installation] with [tag:command-line] or [tag:dependency]:

 - **Unable to locate package**: 

        E: Unable to locate package [pkg]


 - **Package has no installation candidate**:

        E: Package '[pkg]' has no installation candidate

 - **Packages have unmet dependencies**:

        The following packages have unmet dependencies:
        package1 : Depends: package2 (>= x.y) but [pkg] is to be installed
        E: Unable to correct problems, you have held broken packages.

Where `[pkg]` means package-name.


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From which we have already Questions as follows:

 - For Unmet dependencies: http://askubuntu.com/q/140246/256099
 - For Unable to locate package I've prepared (which needs to improve): http://askubuntu.com/q/481354/256099


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For new users of Ubuntu and command-line, further method of installing software properly,

**It needs to prepare FAQ type wiki/solution on above (3) Main/Considerable Q/A.**