Reversals are where a lot of people quietly give up on tarot.
You draw a card, it lands upside down, and you look it up and find the meaning listed as roughly the negative of the upright one. Then you draw a card whose upright meaning was already unpleasant, and the negative of that makes no sense at all, and you start to suspect the whole apparatus is arbitrary.
It is not arbitrary. There are three genuinely different traditions here, they contradict each other, and nobody tells you that you are supposed to choose.
One: the card is blocked
The reversed card is the upright card, prevented.
The energy is present but it is not arriving. The Ace of Cups upright is feeling that pours out and is received; blocked, the cup is still full and the offer is still made, and something is stopping it landing. Not the opposite of love. Love with an obstruction in front of it.
This is the reading that handles difficult cards best. A blocked Tower is a collapse that has not happened yet, and that is a coherent and rather tense thing to say. The opposite of a Tower is not.
Two: the card is turned inward
Same card, aimed at yourself rather than at the world.
A reversed Queen of Swords is not a woman who has stopped being clear. She is being clear in private, or with herself, or nowhere anyone can see. The Sun reversed is joy that has not been let outside.
This is the most forgiving of the three and the one I use most in a spread about a person rather than a situation. It never turns a card into its enemy. It turns the volume down and points it somewhere else.
Three: the card is overdone
The upright meaning, past the point where it helps.
Strength reversed is not weakness, it is force applied where patience was needed. The Empress reversed is care that has become smothering. Temperance reversed is balance pursued so hard it becomes paralysis.
This is the most demanding reading, because it asks you to know where each card's virtue tips over, and that varies by card. It is also frequently the truest one. Most of the trouble people bring to a reading is not an absence of some quality. It is too much of one they are proud of.
Pick one and hold it
They are all defensible. What is not defensible is drifting between them inside a single spread, because then every reversal means whatever you need it to mean, and a reading where nothing can be wrong tells you nothing.
If you want a starting rule: use blocked for situations and inward for people. Come back to overdone when you know the deck well enough to feel where each card overshoots.
What this site does with them
Reversals are on by default and there is a checkbox to turn them off before you draw, on every spread. Turning them off is a legitimate choice and a common one: seventy-eight cards is already a great deal of surface, and doubling it to a hundred and fifty-six meanings is a real cost when you are learning.
One place the site takes a firmer line is the yes or no spread, because there the reversal has to do arithmetic rather than interpretation. The obvious approach, upright means yes and reversed means no, collapses the whole reading into a coin flip and breaks completely the moment someone turns reversals off. So each card carries its own leaning instead, and a reversal flips a card that was committed while leaving a card that was already hedging exactly as hedged. The Ace of Cups reversed becomes a no. The High Priestess, who was never going to give you a straight answer either way, stays unclear whichever way up she lands.
That is a design decision rather than a tradition, and it is written down in the code rather than asserted here, but the principle generalises: a reversal should change what a card says, not replace it with a different card.
The practical bit
You will draw more reversals than feels right, and that is not the deck making a point. Here each card is decided independently at even odds, so a ten-card Celtic Cross averages five of them and a run of five in a row is perfectly ordinary in a way our instincts refuse to accept.
Physical decks are a separate matter and worth knowing, because the usual explanation is wrong. A riffle shuffle does not turn anything over: it interleaves two halves that were both already facing the same way, and a deck riffled a thousand times comes out as upright as it went in. Reversals get into a physical deck because somebody put them there, by rotating half the pack before the riffle, or cutting and turning a portion, or spreading the cards face down and swirling them about. If your physical readings never come out reversed, that is why, and it is a thing you choose rather than a thing that happens.
Either way: pick one of the three readings above, and write down which one you picked. In six months you will not remember, and the journal is there so you do not have to.