You can enter a fractional number in a cell and use it for calculation:
If you enter “0 1/2” AutoCorrect causes the three characters 1, / and 2 to be replaced by a single character, ½. The same applies to 1/4 and 3/4. This replacement is defined in Tools - AutoCorrect - AutoCorrect Options - Options tab.
If you want to see multi-digit fractions such as "1/10", you must change the cell format to the multi-digit fraction view. Open the context menu of the cell, and choose Format cells. Select "Fraction" from the Category field, and then select "-1234 10/81". You can then enter fractions such as 12/31 or 12/32 - the fractions are, however, automatically reduced, so that in the last example you would see 3/8.