It means: The green mountains on both sides of the strait confront each other and the beautiful scenery is indistinguishable. A small boat sails leisurely from the place where the sun rises.
From [Tang Dynasty] Li Bai's "Looking at Tianmen Mountain":
Tianmen interrupts the opening of the Chu River, and the clear water flows eastwards to this point.
The green mountains on both sides of the strait face each other, and the lone sail is coming from the sun.
Notes
Tianmen Mountain: Located on both sides of the Yangtze River in He County, Anhui Province and Wuhu, the one in the north of the Yangtze River is called Xiliang Mountain, and the one in the south of the Yangtze River is called Dongliang Mountain (also known as Bowang Mountain in ancient times) . The two mountains face each other across the river, forming a natural portal, hence the name Tianmen.
Interruption: The river separates the two mountains.
Chujiang: the Yangtze River. Because the middle reaches of the Yangtze River belonged to the Chu State in ancient times, it was called Chujiang. Open: split, break.
To this point: It means that the east-flowing river turns north here. One is "Zhibei". Hui: whirlpool, turn around. It means that the direction of the river in this section has changed due to the steep terrain, and it has become more turbulent.
The green mountains on both sides of the Taiwan Strait refer to Dongliang Mountain and Xiliang Mountain respectively. Out: to stand out, to appear.
Come from the side of the sun: refers to the lone boat sailing from the distance where the sky and water meet. Looking from a distance, it seems to come from the side of the sun.