Avogadros number is the number 6.0221367 x 10^23, commonly rounded to just three significant digits: 6.02 x 10^23, and is the number of representative particles in a mole. Avogadro's number is commonly used to compute the quantities of substances involved in chemical reactions, called stoichiometry, and is one of the most important and versatile components of modern chemistry. Avogadro's number is named after the Italian physicist Amadeo Avogadro. Avogadro's number first came about when Amadeo Avogadro proposed Avogadro's law in 1811. Avogadro's law states that under the same conditions of temperature and pressure, equal volumes of different gases contain an...
multiply by 100 to get a percent:

After doing this, you find out that that H2SO4 is made up of 2.06% hydrogen, 32.7% sulfur, and 65.2% oxygen by mass "Stoichiometry".

As you can see, Avogadro's number is a number equal to a mole, and is used in stoichiometry. This number can be used in many different situations, whether it is finding the mass of a molecule, mole-mole problems, mole-mass problems, mass-mass problems, and percent composition problems. Avogadro's number is used in all these types of problems, and is one of the most resourceful and multipurpose factors of modern chemistry.