So i added two bones to the armature after I parented the armature without those two bones to the mesh. I named them mouth lower and mouth upper, but when I select the mesh they are not in the vertex groups. How do I fix this?
Find out the names of the newly-added bones
It's listed in your Properties Panel, under Item.
Create Vertex Groups on your Mesh with those names
Bones look for vertex groups with corresponding names to deform.
Paint on some weight
You can do this from Weight Paint Mode, or alternatively use the Weight slider to specify a weight before clicking Assign. Always pay attention to which vertex group you have selected when weight painting.