What package is right for my computer?

Ubuntu (like Debian, on which Ubuntu is based) uses .deb packages. HOWEVER, I don't recommend downloading packages and installing them outside of the Software Center if you can help it. Ubuntu Linux is different from Windows or Mac in that regard. You can use the Ubuntu Software Center to search for and install packages, or command line tools like apt-cache and apt-get if you're feeling geeky.

For example, to get the Adobe Flash Player, simply install it via the Ubuntu Software Center. You could additionally install Ubuntu Restricted Extras, which will install other common proprietary media formats like MP3 as well.

As for Avast, it doesn't seem to be in the repositories, but perhaps you could find a suitable alternative such as ClamAV. Also, remember Anti-Virus protection isn't generally needed on a Linux system in the same way it is needed on a Windows system. I run Clam on Linux file and email servers simply to keep viruses from getting passed on to Windows machines that may connect.

Hope some of this helps you.

Ubuntu 11.10 and other Debian based distributions work best with DEB files. Usually TAR.GZ files contain the source code of the program, so you would have to compile the program yourself. RPM files are mainly used in Fedora/Red Hat based distributions.

Though it is possible to convert RPM packages to DEB ones.

Note, make sure you download the correct architecture package for your system. i386 usually means 32-bit OS, x86_64 usually means a 64-bit OS.

First always check Ubuntu Software Center. Flash is available for Ubuntu. If you really really need to newest version you need a deb. Only need to remember that there are 32 and 64 architecture versions.

Regarding avast: if you want it to scan for virri and you only use Ubuntu... forget about it. At the moment the only thing you can use it for is for scanning incomming and outgoing traffic to and from Windows machines inside your network. Avast is not in the repositories so if you really believe you need this download.

DEB file will be the best for you. It's binary version and very easy to install (By Just double click). It will automatically resolve dependency if have any. If you fail to find deb file then you should download tar.gz which is source-code version (not compiled). General way to compile and install tar.gz version is following

1. Extract the tar.gz file
2. Open terminal the and : cd your_file_directory/Extracted_directory
3. ./configure
4. make
5. sudo make install

The process differ from source to source. Most of the source follow this way. To make sure the process read the READ-ME file provided by the developer(in extracted directory)

First, try to find your packages in software center which is default installed with ubuntu.