There are four types of kaons, but two of them are relatively easy to understand. There is the K and the K. The + and 0 above the letter K refer to whether the charge is positive, or 0 (neutral). The K is made of one up quark, and one strange antiquark. Since antiparticles have the opposite charge of their counterpart (and since normal strange quarks have a charge of -1/3), 2/3 + 1/3 = a +1 charge, or simply a + charge. (Also because antiparticles have the opposite charge of their counterpart, if you change the up quark in a K to an up antiquark and the strange antiquark to a normal strange quark, you get the opposite charge, forming a K). Since down quarks and strange quarks have the same charge, if either one of them is an antiparticle, the overall charge is zero. Therefore, a K can either be made of one down quark and strange antiquark, or one down antiquark and one normal strange quark.