Below are some practice of mole problems in Khan Academy. Learn Moles to find the ration of certain compounds which helps us find things such as the limited reactant(a reactant that limits you from making more compounds even if you have lots of other reactants.)

See In Khan Academy

What does learning mole helps you with? You might ask. Well, although atoms, molecules and formula units are very small, mole allows chemists to work with amounts large enough to use. From just doing 6.022x10^23 (The x is the molar mass of the element that you are trying to calculate), it helps chemist to define and change from moles to grams even it they can't see it.

Now try to solve this problem below.

In this problem, how is the molar mass(Molecular Weight) of the H2O equals 18.02? Well, it's the mass of two Hydrogen and one oxygen combined. Which Hydrogen's molar mass is 1.01 each, and oxygen's molar mass is 16.00 each. If there are 24.3 grams of water and each 18.02 gram of water equals to 1 mole of water, then we would use 24.3 grams of water(What we have) divided by 18.02 grams of water(The Mass required to call one "Mole") which would result 24.3 grams of water equals 1.34850 moles of water.
Result: Since in the problem they want us to answer the proble with 3 signficant figures, the actual answer would be shorten to be about 1.35 moles of water in 24.3 grams of water.