Need help- Electrochemistry

I am in grade 12 and since we didn't got too much time our teacher crammed whole electrochemistry in few classes and I didn't understand any of it and now tmrw is exam and I don't know what to do Our syllabus include Electrode potential and standard electrode potential Types of electrodes Electrochemical series Voltaic cell zn cu and ag cu Relationship betwn cell potential and free energy Commercial batteries and fuel cell ( oxygen and hydrogen )

Also I didn't understand.