Rashi: A row of rocks juts out from the wall, close to the ground, with holes, to put pots on them. Underneath the row is a cavity to kindle fire under [the holes under] the pots.

Radak: A stone wall was built around these chambers. It was low, in order to rest pots on it. It had holes, and a cavity underneath to kindle fire under [the holes under] the pots. Targum Yonasan says, ledges are made around all four of them. A place is fixed to cook under the ledge.

Rashi: It is the cavity under where the pots are placed.

Radak: It means that places are made to cook. The grammatical form is like "v'Es Kol ha'Mekateros Hesiru" (Divrei ha'Yamim II, 30:14).