First of all, .tar.gz files cannot be "installed". These files are gzip-compressed tarballs equivalent to .zip files in Windows platform. .tar.gz files usually contains the source of a program and it needs to be extracted before you compile the program from the source. So, to 'install' a .tar.gz file in Linux, you need to extract it first on your hard-drive and then compile the program from the source.
Step 2: Now, use the cd command to navigate to the destination folder where you have extracted the .tar.gz archive.
To summarize up, the process of installing a .tar.gz file includes downloading the file, unpacking it to the preferred choice and then compiling the program from the source.
Note 1: Usually, the installation instructions are provided in the .tar.gz archive in a text file named either 'README' or "INSTALL'. It will include all the installation procedure.
Note 2: Before downloading and compiling a source, why not to search it in the software center. Searching an application in the software center ensures that you download the latest and stable release of that software and you do not have to go through this compilation processes.