Ubuntu Manual

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

  To add any third party repositories,Follow the steps

Go to 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

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

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.