A leased line consists of a four-wire circuit, or two pairs. One pair is for sending data, the other pair for receiving data.
Not entirely sure, but I believe the second question is referring to the function provided by the presentation layer, which defines and negotiates data formats and deals with encryption.
A leased line typically terminates using RJ-48C connector & uses 2 pairs of cables:
Cables - 1&2 for Tx Tip & Ring AND 4&5 for Rx Tip & Ring.
Presentation layer is the one that provides translation services in the OSI model. As stated by Dante, it translates data between different text formats, e.g. ASCII to EBCDIC or ANSI or Unicode etc. Remeber, presentation layer is responsible for the "syntax & semantics" of communication, both negotiation & translation.