The data link layer focuses on the physical addressing of the transmission. It receives a packet from the network layer (that includes the IP address for the remote computer) and adds in the physical (MAC) address of the receiving endpoint. Inside every network enabled computer is a Network Interface Card (NIC) which comes with a unique MAC (Media Access Control) address to identify it.
MAC addresses are set by the manufacturer and literally burnt into the card; they can’t be changed — although they can be spoofed. When information is sent across a network, it’s actually the physical address that is used to identify where exactly to send the information.
Additionally, it’s also the job of the data link layer to present the data in a format suitable for transmission.
The data link layer also serves an important function when it receives data, as it checks the received information to make sure that it hasn’t been corrupted during transmission, which could well happen when the data is transmitted by layer 1: the physical layer.