They are:
Executive: President and about 5 million others - The president enforces the laws.
Legislative: Senate and House of Reps - this part is called congress. Congress makes our laws. Congress is divided in 2 parts; senate and house of reps. Senate is made up of 2 people from each state. House of reps get together and decide if the bills should become laws.
Judicial: Supreme court and lower courts - hear cases that pertain to issues related to the constitution. They are the highest court in the country.