Question

Does anyone know what my spanish teacher means by this?

Answer 1

So the plural forms of ser are

Nosotros somos

Vosotros sois

ellos/ellas son

I assume that your teacher means for you to do sentences like

Los chicos son guapos. (for the boys)

and

Las chicas son guapas. (for the girls)

If you are including yourself in either of these groups you would do something like

Las chicas y yo somos muy simpáticas. (if you are a girl)

or

Los chicos y yo somos muy simpáticos. (if you are a boy)

If you are talking to the group of boys or girls directly I assume you would do something like

Vosotros sois muy tontos. (for the boys)

or

Vosotros sois muy tontas. (for the girls)

I hope this helps!