A General is the highest rank you can achieve as an Officer in the military. There are different levels of being a General...Brigadier General, Major General, Lieutenant General, 4 Star, 5 Star.
A Sergeant is an Enlisted Rank, and E-5 or higher. Sergeants have men assigned under them that they lead.
A private is one of the lower ranks of the Enlisted soldier.
A Lieutenant is one of the lower ranks as an Officer in the military.
A Major is another Officer rank. A Major is higher than a lieutenant as it comes after Captain and before Lieutenant Colonel.