A lot of the properties are identical to these of the text shape because the memo shape descends from it. Some properties are new or work different:
AutoSize
In contradiction to a text shape, autosize now works on the vertical size. When it is on (selected), the memo shape will automatically size itself vertically to accomodate the text.
WordWrap
When checked (default), the text will wrap between the vertical edges of the shape. It will do so on word boundaries, unless this is not possible (for instance, one of the words is wider than the shape). In that case, it will wrap on a letter boundary.
Memo text
Type the memo's text here, or edit it directly in-document by doubleclicking the shape or hitting F2 when selected.