Most of these movements we can't feel, they are much to small to notice. Only seismographs can registrate them. Most of these plates are next to eachother and won't move. Some plates stick together and form large plates, which sometimes abruptly move, causing vibrations in the earth's crust which we might feel as an earthquake. This is due to the flows of hot and less hot rock and material inside the earth.
Tectonic earthquakes are much more powerful than the earthquakes caused by volcanic activity.
From magnitude 4,8 all earthquakes reported have been tectonic earthquakes. Volcanic causes Smaller earthquakes are quite often caused by moving magma below the earth's surface, pushing it's way through. Near by active volcanoes these minor earthquakes are regular and won't cause much damage. Human causes Some earthquakes are caused by human activity. Nuclear bombs will cause seismic waves, not powerful, but they have much more power in them than vulcanic earthquakes.