I agree with Omol. But it depends a bit on what you would like to do with the knowledge. With Javascript you can do a lot of things, just for a "basic" website. But if you want to work with databases that I would suggest PHP. You can do a lot with both, so I guess it's important to learn them, but prior experience goes for PHP and Javascript. In which you have the most experience determines (I think) which language you should learn first...
A good website for learning all kind of languages and terms is: http://www.w3schools.com/
Hope this helps!