UNO is not the loneliest number
To play UNO solitaire, you're going to need a clean table, a full deck of UNO Classic, and a big pile of patience. If you've ever played Klondike, Fascination or Canfield, you'll have a good foundation. To play UNO Solitaire, you'll need to take a few cards out of the deck and memorize the UNO Card Substitute Ranking System.
Card Values and Equivalents
The basic premise of UNO solitaire requires you to slightly alter the makeup of the deck so that you can play in a similar fashion to more traditional versions of solitaire. For all UNO solitaire variants, you'll need to remove the Zeroes. Depending on whether you're going to play Onani or Branlei, you may need to remove the Wild Cards.
For both versions, you'll need to familiarize yourself with the Substitute Ranking System, which is a method that allows you to match the action cards up with face cards of corresponding value and rank.
Once you've got the table memorized (easy mnemomic is that the action cards are in alphabetical order, D - R - S, in reverse rank) you can start playing one of the two most popular variations.
Onani gameplay is pretty much identical to Klondike and can be played with either Vegas rules or Standard rules.
You'll deal out seven cards, next to each other in a horizontal line, with the first one face up. Then deal out six more, putting the first card in the second series face up on top of the second card from the first series. Repeat this pattern until you've built seven piles of cards, the first with one card, the second with two, and so on until you've got twenty-eight cards on the table.
If there are any 1s showing, you can put them in one of eight 'foundation' piles that you'll build throughout the game. Any time you remove a card from the original stack of 28 cards, you must flip over the next card from the stack it came from. Also, at this time, you can stack any cards that are the same color and in descending order on top of each other. For example, if there is a blue 5 and a blue 6 showing, you can put the blue 5 on top of the blue 6 and turn over the top card from the pile that you took the 5 from.
Deal cards from the remaining pile, three at a time, to form a pile of 'discards.' If the top card in your discard pile is either a 1 or is the same color and one number lower than a card on the original pile, you can move it there and evaluate the next card in the discard pile. Once you run out of moves, you put three more cards on the discard pile, repeating the same pattern. When you have moved all the remaining cards into the discard pile, turn it over and deal three at a time again to form another pile. Repeat until you cycle through the entire pile without shedding any more cards.
Same concept as Standard rules, except that you only deal one card at a time and you only cycle through the discard pile once.
Branlei has the same gameplay as Onani with the following differences: there are only four 'foundation' piles and the wild cards remain in the deck. The wild cards can not be placed into the foundation piles, but they can be used as a 'placeholder' card for any card. So Red 6 - Red 5 - Wild - Red 3 is valid, because the Wild card is substituting for the Red 4.
Wild Cards and Wild Draw Four cards are both wild cards without any difference between them.