The Mole:

Given the equation above, we can tell the number of moles of
reactants and products. A mole simply represents Avogadro's
number (6.022 x 1023) of molecules. A mole is similar to a
term like a dozen. If you have a dozen carrots, you have twelve
of them. Similarly, if you have a mole of carrots, you have
(6.022 x 1023) carrots. In the equation above there are no numbers
in front of the terms, so each coefficient is assumed to be one (1).
Thus, you have the same number of moles of

AgNO3, NaCl, AgCl, NaNO3.

Converting between moles and grams of a substance
is often important. This conversion can be easily done when
the atomic and/or molecular mass of the substance(s) are known.
Given the atomic or molecular mass of a substance, that mass in
grams makes a mole of the substance.

For example,

calcium has an atomic mass of 40 atomic mass units. So, 40 grams of calcium makes one mole, 80 grams makes two moles, etc.