Gravity and especially Physics is one of the more advanced topics. If you really need physics be prepared for lots of problems and hard to tune code.
There is no problem of having a player controlled acting like in a physical world (like falling down a bridge), but as soon as you want sphere’s, boxes and other things colliding with each other or the scene you will need some physics engine. Panda supports 3… ode, newton and physx, for samples search the forums.
However if you are starting to work with panda i recommend to start with something else then physics. Depending what you want to create you may find a way not requiring physics (like scripted events, aka intervals)