Proto oncogene are normal genes which are involved in cell growth and proliferation while the oncogenes are genes which have the potential to become cancerous. During cell division, proto oncogenes are strictly regulated, the cell division proceed appropriately and the division is terminated when the cell division is over. The cell division of the oncogenes on the other hand are not regulated, they continue dividing indefinitely.
Using the gas pedal analogy, for the proto oncogenes,it will be GO, GO, GO, STOP. For the oncogenes, it will be GO GO GO GO GO GO [The 'GO' continues indefinitely].