God tells Moses that he shall be a god to Pharaoh and Aaron shall be his prophet. But this won’t work because God will harden Pharaoh’s heart. So they go and do the trick with the Rod turning into snake but all of Pharaoh’s magicians can do that trick too. Then they turn the Nile into blood and it is smelly and no one can drink it, but the Magicians of Egypt can do the same trick, so no big deal, Pharaoh still won’t let the Israelites go.
In other words:
Moses and Aaron do miracles for Pharaoh, but he isn’t impressed.
That Moses is to take on the role of god in an effort to get Pharaoh to let them go. So basically, Moses will be telling Aaron what to do and Aaron will do it and this is supposed to make Pharaoh think Moses is a god.