The Select Filters toolbar allows you to limit the type of entity that may be picked to one or more of the geometry entity types in the Viewport window. Entity types that are not included in the filter will not be selectable while that filter is active. Note that the selection filters are not active during geometry creation.
The final button controls visible entity picking – you may want to be able to only pick entities that are visible in which case you would turn visible entity picking on. Selecting shaded view and wireframe view without hidden lines will automatically turn visible entity picking on. Selecting wireframe view will turn it off.