The difference between やる and する

やる (yaru)

 * More informal: Often used in casual conversations or when speaking to someone younger or of lower status.

 * Conveys a sense of effort or exertion: Implies that the action requires some physical or mental effort.

 * Can imply a sense of giving or doing something for someone else: Similar to "to give" or "to do something for someone".

する (suru)

 * More neutral: Can be used in a wide range of situations, from formal to informal.

 * General purpose verb: Used for a variety of actions, often without emphasizing the effort involved.

 * Can be used with a wider range of nouns and verbs: More versatile in its usage.

When to use which?

 * やる is often used for:

   * Physical activities: e.g., 運動をする (undo exercise), ご飯を食べる (to eat rice)

   * Giving something to someone: e.g、犬に餌をやる (to give food to a dog)

   * Doing something for someone else: e.g、友達を助ける (to help a friend)

 * する is more common for:

   * General actions: e.g、勉強する (to study), 仕事をする (to work)

   * Activities that are part of a routine: e.g、歯を磨く (to brush teeth), 寝る (to sleep)

Example:

 * 勉強をやる (benkyō o yaru) and 勉強をする (benkyō o suru) both mean "to study." However, the first one might imply that you're putting in extra effort or are motivated to study.

In summary:

While both verbs can be translated as "to do," やる carries more informal and connotative meanings, while する is more neutral and versatile.