You can pick up a BBT thermometer easily at a drugstore or somewhere like Wal-mart. Just get one that measures to two decimal places!
I recommend signing up for FF's (FertilityFriend.com) online charting course. They'll email you a new lesson every day for like um.. a week or so that really explains charting very well! Lots of us here also use their website to track our charts. It's easy to just type in your temp and let it do the charting for you
Just take your temp at the same time every morning, after at least 3 hours of sleep, BEFORE talking/getting up/lots of moving/etc. Easy as that!