Let me start with this introduction, which is all my humble opinion.
A lot of books make it seem like you can just memorize upright AND reversed meanings at the same time. Certainly, you can, but I believe that reversals are difficult to interpret - often more so than upright. For this reason, I believe you should be familiar with the upright meanings first and save reversals for later.
Second, let me cover the oft-asked question: are reversals necessary?
The answer is no. Some readers believe that reversals allow for a wider range of meaning and possibilities. Some believe that all cards have positive and negative possibilities, and that the spread and question will inform the reader of what the card means with no need to have any of the cards upside-down. Other readers just find that reversed cards interrupt the flow of their reading, and so don't use them because they just don't like them.
In addition, some readers will use reversals with some decks and not others. And to make matters even more complex, there are some decks created with reversals in mind (the Revelations Deck, for example, which almost requires the reader to use reversals). Other decks will admonish the reader NOT to use reversals, and the backs of the cards will be such to help the reader keep the cards all going in the right direction.
In the end, whether you use reversals or not is entirely up to you. There is no right or wrong about using them.
A frequently asked question about reversals: are reversals always negative?
Answer: No. Reversals do not always mean that something horrible is going to happen or that the situation is awful and hopeless. A spread heavy on reversals may simply be a way for the cards to get a strong message across, or to inform the reader and querent that there is a pessimistic, negative or blocked outlook to the problem. In short, that a change of attitude, beliefs, ways of tackling the problem can restore the energy and get things moving again.
This brings us to the three most common ways to interpret reversed cards.
1) Opposite: the meaning of the card is the opposite of its upright meaning. Frankly, I think this is the weakest and sloppiest of possibilities when it comes to reversals - it's a little too simplistic and has one problem: if a "bad" card is reversed, does that now make it a "good" card? So, reverse the Ten of Swords, Five of Pentacles or Three of Swords and the message is now a good one? We'll get back to that...but the answer is, not necessarily.
2) Blockage: the energy of the card is blocked or diminished. Quoting myself, from an earlier spread on the subject: "One of the best discussions of reversals I recall was one where we theorized that reversals are like running aground or being caught in an eddy. Uprights move the energy forward, as on a river. Reversals indicate that this energy is not flowing."
This means that if the Three of Swords is reversed, then its energy is blocked. If that energy includes communication, however hurtful that communication, then it is being dammed up. The vocalizing of something important is being held back and the results, positive as well as negative, are being held back as well. Nothing can go forward.
3) Upside-down Image. This is where you re-interpret the image given that it is upside-down. So, upright cups are now spilled, and that man in the Ten of Swords - he's actually worse off than when he was upright. Upright, the swords are all in his back - the nightmare had ended, it is over and done with. Reversed, he's on top of them sinking down to their hilts - it's a lingering end, drawn out and torturous.
In the end, reversals are not happy things - but they are, perhaps, important life lessons which teach us far more than if we only got sunny uprights.
Curious about this card when upright? Go to our Tarot Card Meanings.