Celtic Cross spread
The Celtic Cross spread is the most popular one among Tarot readers, to the point that many may be unaware of the existence of others. This popularity is no doubt partly due to the fact it is described in the booklet that comes with the US Games edition of the Rider-Waite deck, which is an excerpt from Waite's Pictorial Key to the Tarot. Rachel Pollack also wrote influentially about it in Seventy-Eight Degrees of Wisdom.
This spread requires a Significator; see that article for more details. In the Edifying Fellowship Tarot generator you can specify the Significator by clicking on it where it appears among the navigation links to the left of the spread (above the spread in the mobile view). You will then be taken to a page showing thumbnails of the entire deck, upright and reversed, and can click on whichever card you choose. This should be done before starting the reading. The generator will by default choose a Significator at random, with a bias towards more often choosing upright cards.
Note that the numbering and sequence of the cards is not standardized, and may also vary depending on the "facing" of the Significator, as described below. The numbers used here refer to the diagram (which is a slight variation of the internal indices used in programming the Edifying Fellowship generator) and do not match Waite nor Pollack, who also disagree with each other. The meanings of the different locations in the spread are more standardized than the order in which they are read.
Card 2: "What covers him"; a general influence permeating the entire reading and through which the querant's actions are filtered. In a reading with physical cards this would normally be placed directly on top of the Significator; in the Edifying Fellowship generator, the Significator is offset a little bit so as to still be visible on-screen.
Card 3: "What crosses him"; forces that act in opposition or create obstacles.
Card 4: "What is behind him." The past leading up to the current situation. Note that if the Significator seems to show a person facing to the left or right, then this card is read on whichever side actually is behind the person on the card, even if not as shown in the diagram. For the many cards which are full-face or show multiple persons, it is necessary to make some kind of choice as to whether to count the left or right side as "behind."
Card 5: "What is beneath him"; Pollack calls it the "basis." This card represents resources available to the querant in dealing with the situation at issue.
Card 6: "What is before him." The current of present events leading into the immediate future. As with the card "behind" the Significator, this card is to be read on whichever side the person shown on the Significator card is facing, if that is meaningfully defined.
Card 7: "What crowns him"; the highest ideal that can be achieved here.
Card 8: the self; the querant's inner feelings and attitude about this situation.
Card 9: the querant's house, and the environment surrounding the question.
Card 10: "Hopes and Fears."
Card 11: the final outcome of the question.