How do you know what app is available from where, and by what name?

[Wade Smart]

12132005 0837 GMT-5

Im still not clear on some things with Linux.
Lets start with this: I like to use Opera sometimes instead of Firefox 
so, I want to download it. But since its not in Synaptic, I do sudo 
apt-get install opera. I receive a message saying its not available by 
that name.

How do you know know what the application you want is named as? Is it 
named as opera and the version number? Or some other scheme?

How do you learn about that?


Thanks.

Wade