When Yahweh says that people will know that he is Yahweh, he is implying that they will know that he is the one true God who has supreme authority and power. See how you translated this in [Ezekiel 6:7](../06/07.md). Alternate translation: "understand that I am Yahweh, the one true God" or "realize that I, Yahweh, have supreme power and authority" (See: [[rc://en/ta/man/jit/figs-explicit]])
The word "they" refers to the inhabitants of Egypt. A walking stick made of a reed is unreliable because it is easily broken. Yahweh speaks of them as a reed stalk because the people of Israel relied on the Egyptians to help them in war, but the Egyptians did not help them. Alternate translation: "they have been as unreliable as a walking stick made of a reed" (See: [[rc://en/ta/man/jit/figs-metaphor]])