It would help if you told us what you're starting with; for example, are you given grams or moles?
If you are given moles, you'll only have to do one step, but if you are given grams, you'll need to convert to moles.
If you're given grams, then you first find the amount of moles. 2 grams of Hydrogen x (1 mole/ 1 gram H) = 2 moles of Hydrogen.
Now that you have your moles, multiply by Avogadro's number to find the number of atoms:
2 moles of Hydrogen x (6.022 x 10^23 atoms/ 1 moles of hydrogen) = 1.2044 x 10^24 atoms of Hydrogen.