In English we can say conduct and conductor. A train conductor is thought to conduct a train from one stop to the next. The verb conduct is turned into a noun by means of the letters -or. Since the conductor is someone who does something to something, he is an agent or doer. In Latin, too, we can take a verb and change it into a noun. Not all nouns are agents. Some are results. Others are abstract concepts.

• For agents or doers of actions the following suffixes are added to verb stems -tor, -trix.
  Example: to the stem vic (from the verb vinco, conquer), add "tor" to get "victor."
  
• For nouns showing activity or condition, add -or to the verb stem.
  Example: to the stem tim (from the verb timeo fear) add "or" to get "timor" (fear).
  
• To show an act or the result of an act, add the suffixes -io, -tio, -tus to the verb stem.
  Example: to the stem coniura (from the verb coniuro, conspire) add "tio" to get coniuratio (conspiracy).
  
• To show an act or something connected with an act, add -es, -tura, -(t)ium to the verb stem.
  Example: to the stem caed (from the verb caedo, kill) add "es" to get caedes (murder or slaughter).
  
• To show means of instument, add -men, -mentum, -bulum, -(c)ulum, -brum, -crum, -trum to the verb stem.
  Example: to the stem no (from the verb nosco, know) add "men" to get nomen. The name or "nomen" provides of means of knowing.
  

Source: A Manual of Latin Word Formation, by Paul R. Jenks, Boston 1912.

Latin Grammar Tips