Facial expression

hi! im a new member here, like the rest of you im in need of help too.
so this is my problem.
recently class just started for me, my english teacher yesterday gave us some pictures telling us to say about their facial expression.
my class responded with happy,sad and some other emotional stuff.
my teacher doesn't want us to describe their emotion but rather want us to describe their facial
expression.
to think of it, i have no idea on how to describe it .(its time to improve my english)
so heres am example i heard from class: His mouth is a gape.
i guess it means that his mouth is opened widely.
i need more help on describing it.
do you guys have any website or some help on this?
thanks alot.

Expressions are tricky. You can say something as simple as "he smiled," or something as strange as "His huge grin lit up his face. It looked like he'd need a new face."

Expressions are tricky. You can say something as simple as "he smiled," or something as strange as "His huge grin lit up his face. It looked like he'd need a new face."

Expressions are tricky. You can say something as simple as "he smiled," or something as strange as "His huge grin lit up his face. It looked like he'd need a new face."

thanks for the rapid reply.
i guess thats pretty much of what im asking for.
so maybe i could use this examples too?
he has a faint smile or something like that?
his eyes are popping out?
his face immediately turned red when he saw his beloved one walk past him.
if this few examples are ok to describe their facial expression, i guess i know how to use them then.