Learning the Carnot Cycle: 4 Steps Explained

[Tin Yeung]

I am learning the Carnot Cycle but I still get confused about this cycle.
There are four steps in this cycle.
1)Isothermal expansion
2)Adiabatic expansion
3)Isothermal compression
4)Adiabatic compression

After step one, we got the heat from heat reservoir through expansion but I don't understand how step 2 occur? Does it expand due to the remain heat in step 1?
Also, do we need to do work in step 4 to finish this cycle?

 

[Chandra Prayaga]

In step 2, the system spends internal energy to do work. No heat is involved. In step 4, work is done on the system, which increases the internal energy. Again, no heat is involved.