Who was Ravshake?
Refer to Melachim II, 18:17:2:1 and the notes there.
Here it says that that he sent Ravshake. In Melachim II, 18:17 it says that he sent Tartan, Rav Saris and Ravshake!
Rashi (37:36), Radak (Melachim II, 18:17), both citing Seder Olam 23). The first time, only Ravshake went, like it says in Yeshayah. The second time, he sent also Tartan and Rav Saris. After this, Ravshake found Sancheriv fighting Livnah (37:8).
Radak (Melachim II, 18:17): Ravshake was primary. The others were secondary to him. We find that only Ravshake talked.
What are "Te'alah" and "Berechah"?
Rashi: They are, respectively, a trench, and a man-made pit filled with water, to hold fish; it is long and wide.
Radak (Melachim II, 18:17): Berechah is a pit to hold rainwater. It is made with rocks and plaster. It had a hole that was normally plugged up. The Te'alah was a pit nearby. When they wanted water to drink or for laundry, they opened the hole to fill the Te'alah from the Berechah.
What is "Mesilah"?
Rashi: It is a paved road.
Radak #1 (Melachim II, 18:17): It is a stone road, so one can go on it [easily, even] in winter [when earthen roads are muddy].
Radak #2 (Melachim II, 18:17): It is an expression of elevation, like "Solu la'Rochev ba'Aravos" (Tehilim 68:5). It was an elevated place in the field, fixed with stones, where people laundering in the Te'alah stood.
Why did he send Ravshake to the Berechah?
Malbim: Chizkiyah stopped up the springs and brought water into the city; he was preparing for war. This was Sancheriv's justification to fight him; the closed Berechah proved that Chizkiyah annulled the Bris!
What is "Sede Choves"?
Rashi citing Targum Yonasan: It is a place where launderers spread out garments [Radak (Melachim II, 18:17) - to dry].
