The difference between these verb sets is "transitivity." In Japanese, you'll have many pairs of verbs and they are often referred to in Japanese Grammar books as "transitivity pairs." You'll learn to notice the difference between two verbs in such a pair by how they are used in a sentence and by the particles that accompany them. What is meant by "transitivity pairs" is that you have one verb in the pair that is "transitive (the verb acts on an object)" and "intransitive (the verb does not act on an object)." 始める - to begin (transitive) - 彼らは会議を始めた。 (They started the meeting) In order for a verb to be transitive, the subject has to cause an action to happen through its own effort. Which is what happens here since "they" are the ones that "started" the meeting. A clue that this sentence is transitive is that the object affected by the verb is signified with the particle を. 始まる - to begin (intransitive) - 今日は彼の誕生日のパーティーが1時に始まる。(Today, his birthday party will start at 1 o'clock.) In this case, the action of begin happens on its own without the effort of an outside force and is thus intransitive. A clue that this sentence is intransitive is that event or circumstance that the verb is modifying is paired with the particle が. 止める - to stop (transitive) - 彼女はタイマーを止めました。 (She stopped the timer) 止まる - to stop (intransitive) - なぜか僕の車が途中で止まった。 (For some reason, my car stopped on the way) I think you can work out these two verbs through the examples given my former explanation. I hope I made everything clear. If you have any more questions, please let me know.