have you done a modo tutorial because its sounds to me like you're in item or material selection mode. try pressing the spacebar to go through the different selection modes; vert, edge ,poly; then you should be able to edit your geometry.

also you may have to doubleclick the file name (group) FIRST to allow editing if you don't know which object is which. this will allow editing of all objects in scene not just the selected one.

keep in mind Modo is very complex and not easy to get used to, so if you're new to 3D probably not the best place to start.