Circle with a star — for Oberschütze (senior shooter).
Angle on a triangle patch — for Gefreiter (private 1st class).
Double-angle on the triangle — for Obergefreiter (like senior lance-corporal).
Usually sewn on the left sleeve at the level of the breast pocket, in the middle. If you shift the patch slightly forward, it will be better visible.
Patches on Feldgrau backing (main uniform colour) appeared in 1940 replaced similar patches on dark-green background. In practice replacement went slow and dark-green patches were common until 1942.
Waffen-SS used the same chevrons but on black. All tank crewmen had also black arm insignia.