Card Evolution
THIS IS A STOPGAP EXPLINATION FROM A NOOB, IN PLACE OF A KNOWLEDGEABLE PERSON WHO WILL HOPEFULLY COME ALONG WITH BETTER INFO
Card Evolution is the Digimon forms that can be attained via cards, rather than the natural evolution line of each Digimon. Evolution cards can be found in various locations such as boxes in dungeons, mystery boxes from the event server or from the Digimon itself as a drop if said Digimon if found in the wild and can be fought. Details of each of these evolution lines for specific Digimon can be found in-game in the Digimon encyclopedia (Default shortcut V) by double-clicking the Digimon icon and clicking on the "Card Digivolve" tab. You can then double-click the desired form, go to the "Details" tab and scroll to the bottom to see where the Digimon can be found if it appears in the wild. At the moment it is unknown if all Digimon in the wild drop cards, but most standard ones do.
Cards drop at various levels ranging from 1-5, with 5 being a 10% chance of evolution success and a 1 being 100% chance. You can also combine lower level cards into higher level cards. If a card evolution fails, the Digimon will be turned into a Raremon and will require an Evolution Return item to be returned back to the original Digimon, although there are 2 different versions of the Evolution Return item, with one keeping any priorly successful card evolutions intact with the other restoring it to the original evolution line completely.