After you've installed packages, you'll be presented with the login prompt. Log in using the personal login and password you selected. Your system is now ready to use.
If you are a new user, you may want to explore the documentation which is already installed on your system as you start to use it. There are currently several documentation systems, work is proceeding on integrating the different types of documentation. Here are a few starting points.
Documentation accompanying programs you have installed is in /usr/share/doc/, under a subdirectory named after the program. For example, the APT User's Guide for using apt to install other programs on your system, is located in /usr/share/doc/apt/guide.html/index.html.
In addition, there are some special folders within the /usr/share/doc/ hierarchy. Linux HOWTOs are installed in .gz format, in /usr/share/doc/HOWTO/en-txt/ and /usr/share/doc/HOWTO/en-txt/mini/. The /usr/share/doc/HTML/index.html contains browse-able indexes of documentation installed by dhelp.
One easy way to view these documents is to cd /usr/share/doc/, and type lynx followed by a space and a dot (the dot stands for the current directory).
You can also type info command or man command to see documentation on most commands available at the command prompt. Typing help will display help on shell commands. And typing a command followed by --help will usually display a short summary of the command's usage. If a command's results scroll past the top of the screen, type | more after the command to cause the results to pause before scrolling past the top of the screen. To see a list of all commands available which begin with a certain letter, type the letter and then two tabs.