Grignard reagents react with a variety of carbonyl derivatives.
The most common application of Grignard reagents is the alkylation of aldehydes and ketones, i.e. the Grignard reaction:
Note that the acetal functional group (a protected carbonyl) does not react.
Such reactions usually involve an aqueous acidic workup, though this step is rarely shown in reaction schemes.  In cases where the Grignard reagent is adding to an aldehyde or a prochiral ketone, the Felkin-Anh model or Cram's Rule can usually predict which stereoisomer will be formed.  With easily deprotonated 1,3-diketones and related acidic substrates, the Grignard reagent RMgX functions merely as a base, giving the enolate anion and liberating the alkane RH.
Grignard reagents are nucleophiles in nucleophilic aliphatic substitutions for instance with alkyl halides in a key step in industrial Naproxen production:
Grignard reagents also react with many "carbonyl-like" compounds and other electrophiles: