Check engine light on, code P0336

Hi there! My check engine light came on about 2 weeks ago - in that time I've not noticed anything wrong with my car. Now that I'm off work for several weeks for summer break and it's time to renew my registration (and, in California, I need to do a smog test this time around. I've read that it will not pass with any check engine light on). I took it to an auto parts store to read the code - P0336. As a single mom without a whole lot of disposable cash. Are there any relatively easy fixes or something I should look for? I've become fairly handy the past few years. Last summer my 13 year old and I replaced the spark plugs, wires and some hoses courtesy of online forums and videos. But, looking at replacing some of the things suggested in the printout from the store seem out of the range of what I can do. Are there some things I can check first that may be smaller fixes for this issue? Thank you so much for any advice!