Both php and jQuery are similar so when you learn one the other becomes a little easier to understand. Personally I'd concentrate on php first and then some simple jQuery.
JQuery is far easier than learning javascript although they are one of the same. JQuery uses a core framework which makes the essentials that you may need to integrate into your page a lot easier to implement.
Both open up huge options which you will wonder - how on earth did I manage without them.
Good luck.