That's a zip file.
Inside that should be a few folders. One is named "10_3_r183_90".
Inside that folder is a flashplayer_10_3r183_90_mac_intel.dmg
Double click that and it will mount on your desktop, and open a window with the installer.
Right click the installer and choose "Show Package Contents"
Go to: Contents/Resources and double click the Adobe Flash Player.pkg file
The installer will open, ask for your Admin password, and it will install.