Enables you to select the alignment for flanges:
Inner flange -- the flange is completely internal relative to the selected edge.
Outer flange -- the flange is external relative to the selected edge
Outer flange and bend -- the bend and the flange are external relative to the selected edge.

Keep inner base and Keep outer base
Enables you to maintain the constant length of the base (face on which flange command is applied), as shown in the images below. The red dashed line in the following two images represent the internal and external length of the base, respectively.

Keep inner base selected	Keep outer base selected