You have a mix of older US Army insignia.
The black O.C.S. pins at the top, far right were used by soldiers going through the Officer's Candidate School in order to become officers.
The rest of the black pins are rank insignia that could date from around 1970 to about 2000 when the Velcro-backed or sew-on rank insignia was used exclusively.
From the left: The shield-shaped insignia with the eagle in the middle is the insignia for the rank of Specialist (E-4), It was called Specialist 4th Class until around the 1980s if I remember correctly. Abbreviated it is SPC, or SP4.
The single chevrons are the insignia for the rank of Private, E-2. Abbreviated it is PV2. This is the second lowest rank in the Army. Most soldiers make this rank by the time they conclude their training.
On the far right you have one Specialist 4 insignia, and the ones with the additional arc at the top are insignia for Specialist 5, or SP5. These were also done away with sometime around the 1980s.
At the top, on the far left you show the back of a typical early-WWII or pre-war screwback enlisted collar disk. If it has crossed rifles on the front, then it is indeed for an infantryman.
In the middle in the top row is the insignia for the rank of Staff Sergeant (E-6), abbreviated SSG.
Enlisted military ranks correspond to various pay grades: E-1 through E-9. E-1 being the lowest and E-9 being the highest.
You can search on this forum or on the internet and find out more about the different rank insignia, pay grades, etc.