Before I explain a dictator I'll explain the general outline of the hig level goverment in the Roman Republic. It was run by 2 consols (like a presedent) each voted in for a term on 1 year, and on paper they weren't allowed to become consul again for 10 years. Each console had the power to veto the other, so for anything to occur they both had to be in agreement.
These were put in place after the bad events of Rome's kings. It was so no man could hold too much power for too long (please not this is an oversimplification there are other reasons).
The dictator as stated was only elected in times of great crisis, they had supreme power and authority (could do whatever they wanted). As because having all decisions having to come from an agreement between 2 people who probly don't even in the same political party (or the ancient equivalent) slowed things down significantly.
