That's a broad question!
The minimum requirement for a biography on WikiTree is to provide sources for the facts claimed in the data section. This can be done either as bullet points (an asterisk in the edit translates to a bullet in the viewable text) or as a narrative.
WikiTree prefers but does not require inline citations of the sources in the biography text. These will then appear under Sources in the viewable text. Alternatively, the sources can be listed under Sources, but this is really suitable only for very short and simple biographies with few sources to list.
The main point is to link each fact to its source.