See this narrative explained in the notes at Matthew 14:13-21.

By ship - By a boat or a small vessel.
Privately - Without making their plan known. They intended to go privately. It appears, however, that their intention became known, and multitudes followed them.

And they departed into a desert place,.... Which belonged to the city of Bethsaida, Luke 9:10,
by ship, privately; over some part of the sea of Tiberias, this place lying on a more remote side of it.

And they departed into a desert place by ship privately--"over the Sea of Galilee, which is the Sea of Tiberias," says John (John 6:1), the only one of the Evangelists who so fully describes it; the others having written when their readers were supposed to know something of it, while the last wrote for those at a greater distance of time and place. This "desert place" is more definitely described by Luke (Luke 9:10) as "belonging to the city called Bethsaida." This must not be confounded with the town so called on the western side of the lake (see on Matthew 11:21). This town lay on its northeastern side, near where the Jordan empties itself into it: in Gaulonitis, out of the dominions of Herod Antipas, and within the dominions of Philip the Tetrarch (Luke 3:1), who raised it from a village to a city, and called it Julias, in honor of Julia, the daughter of Augustus [JOSEPHUS, Antiquities, 18.2,1].

Departed into a desert place. An uninhabited place; in this case the small plain of Butaiha, just east of where the Jordan enters the lake of Galilee.

They departed - Across a creek or corner of the lake.