Complex sentence: AoPS publishes a series of mathematical creative problem solving textbooks, in a range of difficulties and hosts an online bookstore, selling books from the Mathematical Association of America (MAA) and from various math competitions such as MathCounts and the AMC.
Split into simpler sentences: AoPS publishes a series of mathematical creative problem solving textbooks, in a range of difficulties. AoPS also hosts an online bookstore, selling their own books as well as books from the Mathematical Association of America (MAA) and other various math competitions such as MATHCOUNTS and the AMC.