• To install any software in Ubuntu simply Goto system-->administration-->synaptic package manager,then search for the package or application you want to install .Right click the application and mark it .Apply the changes.

• You could also install the software using command line option.Simply goto applications-->accessories-->terminal and type the following.

• To remove an application from your system simply goto system-->administration-->synaptic package manager and then search for the package u want to uninstall.Then right click on the package and unmark it .Then Apply the changes.
• You can also uninstall the package using commad line option.ie goto applications-->accessories-->terminal and type the following

                           sudo apt-get  --purge autoremove package
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  To add any third party repositories,Follow the steps

• Go to
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  System-->Administration-->Software Sources-->Third-party software-->Add
  

• Enter the name of  repository you want to add

Their is an option to update the system without using command line.Follow the steps to know how to use update manager
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• Go to system->administratin->updatemanager

• check for updates available  and then install updates(Ensure that the correct repositories are enabled before installing by going to System --> Administration --> Software Sources) 

• It is important to have the system updated with the latest patches, security fixes and package upgrades from the repositories.

• Ensure that the correct repositories are enabled by going to 

               System --> Administration --> Software Sources

• Then open the command-line terminal:

               Applications --> Accessories --> Terminal

• Update the repositories by typing the following command

               sudo apt-get update
 
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• Aptitude is a menu-driven version of apt. It is invoked from the command-line terminal.

            Applications --> Accessories --> Terminal
 
            then type aptitude in terminal and press enter 

• Open a command-line terminal:

            Applications --> Accessories --> Terminal

• Search for a package-name in the cache.

            sudo apt-cache search <package-name>

• Open Synaptic:

             System --> Administration --> Synaptic Package Manager

• Press the Search button and enter the search item.