“and he said to me.” The “he” in this verse is Yahweh, as is made clear in the context.
“broad valley.” The Hebrew word biqah (#01237 בִּקְעָה) refers to a broad valley or a plain. Apparently it was a broad valley, and it is mentioned again as “the valley” in Ezekiel 37:1, and when God showed it to Ezekiel then it was full of dry bones.
There were many times when God revealed Himself to Ezekiel and other prophets right where they were, but there are times when it is important to be alone, and this was one of them. Ezekiel’s commission was important for Israel and His prophecies important for the people then and for future generations, and God took Ezekiel alone into the valley and spoke clearly to him about his mission and ministry. For the other great event that took place in this valley between Ezekiel and God, see Ezekiel 37 and commentary on those verses.