Curriculum/la

Okay. I'm a fairly bright person, but I must admit, rather embarrassingly, that I cannot for the life of me wrap my mind around the differences between "curriculum" and "curricula." I know that -um is singular and -a is plural...but what exactly does that mean in regards to my set of material choices? All that I piece together for the year is my curriculum, correct? But, if I am referring to a warehouse full of vendors of homeschool products, I would rightly exclaim, "My what an abundance of curricula!" Right? Where I get confused is when I am referring to different materials inside my pieced-together curriculum. Consequently you'll find me referring to said items as "programs" or simply "materials." Whenever I see someone using the word curricula (rightly or not, because how would I know) I always feel a little bit intellectually inferior. So, there...I've revealed my kryptonite. Try not to use your knowledge against me. :)