Learning about architecture involves absorbing a fair few technical terms. As with identifying trees - my present hobby - the best thing is to go round looking at real buildings with a handbook and try out the naming of parts. Here are some recommendations.
Matthew Rice, Rice's Architectural Primer. This is the one I'd start with. Really helpful watercolour drawings which clarify parts of buildings and the different styles. If you're interested in domestic architecture (which tends to get overlooked in academic courses) then his Village Buildings of Britain is another treat.
Glossaries
It's always handy to have a glossary and / or illustrated history to turn to. A handsome printed one is: Owens Hopkins, Reading Architecture. I also consult Lever and Harris, Illustrated Dictionary of Architecture 800-1914. Though the title doesn't say so, this covers English architecture exclusively. It's well worth tracking down a second-hand copy. For a richly illustrated tour through Western buildings, an excellent book is Doreen Yarwood, A Chronology of Western Architecture.
Here are two (of many) online glossaries. You could try drip-feeding yourself on a term a day from these:
Buffalo Illustrated Architecture Dictionary
Roberta Barresi, Architecture Glossary
Classical
Learning the classical language - columns, orders and so forth - is a logical first move in studying Western architectural history. A classic, and handily short, text is John Summerson, The Classical Language of Architecture. This helps you not just to name the elments of buildings, but to think about their effects. A useful accompaniment is this online Glossary of Classical Architecture. The Looking at Buildings site has plenty of clear explanation.
Churches
Studying architecture in the West involves looking at an awful lot of churches, so it's a good idea to have something that focusses on this: Mcnamara and Tilney, How to Read Churches is very well illustrated. Matthew Rice has one coming out next year, which I'm sure will be excellent: Rice's Church Primer
