What is a beginner's guide to reading tarot cards?
I'm not sure what knowledge base you have to draw from regarding tarot, so I'll give you a quick basic rundown. There are two segments or sections within the standard 78-card deck. It has 22 Major Arcana cards and 56 Minor Arcana cards. Within the 56 Minor Arcana, are 16 Court Cards. The Minor Arcana are further sectioned by suit: Wands (fire), Cups (water), Swords (air), Pentacles (earth). They are numbered Ace through 10 and then Page, Knight, Queen, King or some variation of that.
I'm a fan of Fortune's Wheelhouse, a free podcast online examining the esoteric symbolism of the Rider-Waite-Smith tarot deck and the Thoth tarot.
If you're just introducing yourself to tarot, I'd say Aeclectic Tarot Forum has good resources on card meanings. It's closed down now, but it still has the card meanings and threads up if you want to take a look there.
If you want a pop introduction to tarot, you can look at the free resources on BiddyTarot, the website as well. I think Biddy tarot is a good place to start, because it's very accessible to someone beginning to read tarot. If you don't know anything about tarot, other than it's a deck of cards, she's a good resource to walk you through an introduction.