Nucleophilic attack - Electrons flow from the nucleophile to the elctrophile. Nucleophilic attack can have one or more arrows depending upon the nature of the electrophile.
The electrons end up being sharing rather than transferred. Note that the electrons in the anbove case become the bond between the Cl and the C atom of the elctrophile.
Nucleophilic attack may require more than one curved arrow.
This transformation could also be thought of as nucleophilic attack on a resonance structure, which needs only one arrow.
Recall that a π bond can also act as nucleophile.