Which two functions or operations are performed by the MAC sublayer?

It is responsible for Media Access Control.
It adds a header and trailer to form an OSI Layer 2 PDU.

Refer to curriculum topic: 5.1.1 The MAC sublayer is the lower of the two data link sublayers and is closest to the physical layer. The two primary functions of the MAC sublayer are to encapsulate the data from the upper layer protocols and to control access to the media. *##**##*