For a given chemical reaction, the addition of a catalyst provides a different reaction pathway that does what?
Lowers the energy of activation required to get you to the transition state.
Catalysts simply help to lower the activation energy. This is the energy that you need to overcome to get the ball rolling to products. Think miniature golf - hitting the ball over a ridge. The energy of activation is getting the balls to the top of that ridge - a catalyst is like drilling a hole through the ridge so the ball has to rise less high.
For a basic example - at any given temperature, you have a small population of reactants that have enough energy to overcome this barrier and react. But not a large population. Imagine like crickets trying to jump out of a bathtub. One, maybe 2 can do it, but most can't.
Now if you heat the reaction up, more of the molecules have more energy and you have a larger population of molecules that have enough energy to react. For the crickets, this might be like adding a cricket-eating monster and scaring them - some will find a bit more ability to jump and get out!
Now a catalyst, this just lowers the activation energy, or the energy those reactants need to achieve to react...so at a given temperature, in the presence of a catalyst, you have more population that can react. For the crickets, it is like drilling a hole in the side of the bathtub half way up. Before, you only had 1 or 2 that could jump out, but now you've got a lot more than can make the jump.
Hope that helps.