I know my answer is a year late but I hate the idea that every time I check out Internet forums most answers are darn wrong and utterly miss the point.
Using flash in Opera (most versions) is quite simple.
1. Download the latest flash player (tar.gz) compressed file format and unpack
i.e.,
Code:
tar xzvf libflashplayer-10.0.32.18.linux-x86_64.so.tar.gz
[b]2.[b] Copy the file libflashplayer.so wherever you want. Preferably $HOME/.mozilla/plugins where it can be found by mozilla alike browsers. Here $HOME is a system variable which points to /home/your_user_name directory.
3. Run Opera and go to TOOLS -> PREFFERENCES -> ADVANCED -> CONTENT and inside content click on the button PLUG-INS OPTIONS. There you should ADD the new path $HOME/.mozilla/plugins and that's it.
Opera will use flashplugin the next time if you followed correctly this steps. You can even tell it to FIND NEW PLUG-INS (after the path were you put the plugin was added) and it will be recognized immediately.
What we have done so far was: Creating a directory for our plug-in and make Opera recognize it.
PS:// Just remember not to abuse sudo (as suggested above) you should not use sudo for external or extraneous things. Your system can be compromised that way!!.
PS2:// When you get the expertise please try to support free/open/gratis projects like SWF and GNASH or even try them to help testing at least.
It is very important to preserve our freedom of usage and choice overall.
http://www.gnu.org/software/gnash/