And Aaron spake all the words which the LORD had spoken unto Moses, and did the signs in the sight of the people. Aaron spake all the words - It is likely that Aaron was better acquainted with the Hebrew tongue than his brother, and on this account he became the spokesman. See Clarke on Exodus 4:14 (note).
Did the signs - Turned the rod into a serpent, made the hand leprous, and changed the water into blood. See Clarke on Exodus 4:6 (note) and Exodus 4:8 (note).