Is it possible to snap 1 or more vertices on a face? I´m fairly new to Blender and currently model a scope. Now I have the following situation.  

I have angled faces and a cylinder. I want the vertices marked in the first picture to snap on the faces marked in the second picture.

I tried it with "g" and selecting the vertices of the face(s) with "a", but then the vertex is positioned either inside the scope or not touching the face at all.
Thank you!
You can do this with the snap tool.

First, modify snapping behavior to Snap to Face like so :

 (toolbar on the top of the viewport screen)



In edit mode, select all the vertices you want to snap to the faces.

Then go into orthographic mode (numpad 5), align view to the "x" axis (numpad 3)



Type G (to move the vertices) and X to constrain to the x axis, and move your mouse to the right a fair bit, Hold CTRL (to force snapping), then click. You will not see any change in the viewport but if you orbit around your objects you will have this result :