GE - Gender Expession
SO - Sexual Orientation
Its a bit complicated to explain to people who has zero knowledge about being a transgender person. The earliest simplest expression was "trapped inside a man's body for transwomen" and for trans men "Trapped inside female body?" But now there another method to explain it as we progress. Its called SOGIE that stands for Sexual Orientation, Gender Identity and Expression.
Sexual Orientation is to explain who you are strongly attracted to which is being gay,lesbian,bisexual,pansexual,asexual.
Gender expression - masculine to feminine (your naturale expression, some female identified person is masculine in her body language and expression, and some male identified person is feminine in his expression.
'Gender Identity' is to express being a transwoman or transman are all about. Like for transwoman (a person who assigned a male by doctor after birth but later as she growing up feeling extremely discomfort with her body & take further steps to change or synchronize, according to her identity) and also likewise for transman (Being assigned by doctor female at birth then feeling extremely discomfort with his body & take further steps to transition to his trueself and adopt male identity.)
G.I. - Gender Identity
G.E. - Gender Expression