A good site if you don't have a stamp catalog. But it seems to me that unless you know what country to look under, that website is not of much use to beginners.
As near as I can figure, these are the three stamps:
The stamp on the left is Russia, Scott # 229, 2007 catalog value $2.25.
The center stamp looks to be a stamp issued for use in Turkey in 1921 by the anti-Bolshevik Russian forces which had retreated into Turkey. Scott # 345, 2007 catalog value $0.20, but so damaged that it is pretty much worth nothing.
The stamp on the right has a trident overprint, so it is a Russian stamp overprinted to become a stamp of Ukraine. Probably from Kiev, probably Scott # 18f with a 2007 catalog value of $0.25.