Microfiche and microfilm are two different types of microform. Microform is a way of preserving large amounts of documents in a very small (or micro) format. Think, for instance, of film negatives - that's what microfilm is like. Microfiche is the same concept, but on cards, rather than reels.
The Law Library has an extensive microform collection, and it can be found on the ground floor. The microform readers are on the right-hand side of the room, and the microform itself can be found in the filing cabinets in the middle of the room. There are binders on top of those cabinets that you can use to look up the microform collection you're looking for and discover what drawer in the filing cabinets contains your microfilm or microfiche.
If you have any questions or require assistance, please come talk to one of the librarians - we're happy to help.