Think of a schema like the header row of an Excel table!
A schema defines fields. Fields have short names, such as en, PoS, de as well as a type. A field type can be either text, audio or image.
For all language categories there are two predefined schemas provided by SoYouLearn, so called official schemas. One is for defining translations with the part of speech, audio for both words and an image.
A flash card then defines the entries for each field of the schema. A query defines which fields to display, prompt and display after your answer.