what does it mean when i download updates and it says I'm not connected to a power source

It probably means you are running your MacBook Pro off its battery, and you don't have it connected to the power adapter. You should have it connected to the power adapter when you do critical things like system updates, because if you battery happens to be low and it runs out of power during the update process, your system may become unusable.

also so should i download this lion thing

At this point, you probably mean Mountain Lion. It seems to be a solid initial release. There would be no harm in waiting a few more weeks until the 10.8.1 version is released, to fix any "big" bugs that are reported from the initial release.

Before you upgrade your system, you should have a backup. If you use the built-in Time Machine feature, you are fine for having a backup. With a Time Machine backup, you can restore back to your previous system if something goes wrong (or you don't like Mountain Lion for some reason).

Also, as a precaution, you can run Disk Utility (in Applications/Utilities). Select "Macintosh HD" in the sidebar, and go to the First Aid tab. Use Verify Disk. If Verify Disk reports any errors, you need to get that resolved before performing a system upgrade.