Installation is pretty straightforward. Once you have unpacked the files (and if you are reading this, you've done that) and put the files on your server, make sure the image directories are writable by the webserver. The database you are going to use must exist, though the installation script will create the tables and install some sample data.
Assuming you haven't renamed any directories, review and edit the config.php file found at /server/path/to/domain.com/portfolio/portfolio_app/config.php. It's well commented and not too hard to follow through.
Then point your browser to www.yourserver.com/portfolio/portfolio_app/setup/ and follow the on screen instructions.
Important: It is very important for the security of your portfolio to make the setup directory unreadable (chmod 000), or to back it up and remove it from the server, when installation is complete. If you need to re-install phpPortfolio to it's defaults later, you can restore the setup directory at that time.