rosmake can't find my packages

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Hi, I'm using Hydro on Ubuntu 12.04. I've been going through a lot of tutorials and online projects to get more familiar with ros, and haven't been having problems. I recently loaded the tum_ardrone packege which includes running

export ROS_PACKAGE_PATH=$ROS_PACKAGE_PATH:`pwd`/ardrone_autonomy

since then, whenever I use rosmake I get the error

[ rosmake ] WARNING: The following args could not be parsed as stacks or packages: ['learning_ps3joy/']

[ rosmake ] ERROR: No arguments could be parsed into valid package or stack names.

I've seen people ask this question, and the answer is to run some sort of export command like the one above, but I'm unclear about how to do it, and why i never had this problem before. I have also seen a lot about the ROS_PACKAGE_PATH, and wanted to know if anyone could tell me how to see what it is on my computer, how to change it, and how to make sure packages I'm making are on it, if that makes sense? Thanks