For future usage: if building a set, I recommend using Bricklink to look up part numbers (especially useful to determine which type of specific a/b/c/d variants of a part is used); if building a MOC, I recommend running LDD in the background to look up part numbers quite easily if you're used to the subcategories, which is quite a lot faster than browsing them on MB.

Second for furure usage: If you want to know in which category a specific part is, go to the "Parts" page and search for it and you will see the category, which you don't do if you search in the workshop.