What browser are you using?
If you are not using firefox or mozilla try that and see if you get the same error.
if you do, go to this site from your linux computer http://java.com/en/download/ and see if it shows up with what it can install, and follow any instructions for installing it on your computer.
But if you are using irc, I suggest using xchat, look through your menu (like the start menue in winows) for a internet sub directory, then look for an application called "x-chat" or "xchat" you can use that for IRC.
when installing programs I think fedora/red hat has an rpm manager program or something of that sort to install programs from rpm files you have downloaded. Try looking online for more insturctions ( http://google.com/linux for some good linux related searches)
And when installing from source, check the website and/or any read mes that came with the files you downloaded or where you got the file from.
Many linux applications that I have dealt with will want you to extract the tar file to a seperate folder, then going to that folder in the comman line (at the terminal type cd /folder/folder to change to the directory, also do a ls command to list all the files in the directory to make sure you are in the right one) then when you are in the base directory of the files you just extracted, usually you type ./configure then when that is finished type make install and then make you might have to be root to do the make commands.
but learning linux invovles a lot of trial and error, screwing things up, learning form your mistakes, and lots of reading.