U/RU verbs vs Noun+Suru verbs

Question

When I learn new words in Japanese (using jisho.org), I often see a verb like for example "to drive" as 乗り回す and 運転する, "to study" as 学ぶ and 勉強する, "to understand" 分かる and 了解する, why ?? Why is there for the same English verb both a verb and another as Noun+suru in Japanese ? Do we use both of them as we want, or is there a rule to know what verb to use ? Do they mean the same thing ? Is there one that is more often used ?

I'm confused, and because there is a lot of English verbs that has 2 translation in Japanese, it makes the study of the language harder. Thank you :)

Answer 1

The verbs with する (aka suru-verbs) are part of Sino-Japanese vocabulary (aka 漢語 kango). Ones without する are part of native Japanese vocabulary (aka 和語 wago or Yamato kotoba). If you already know on and kun readings of a kanji, you can see most suru-verbs use on readings, and most u-/ru-verbs use kun readings.

Therefore, the basic tendency is that suru-verbs, as kango, look stiffer, more technical or academic. U-/ru-verbs, as wago, are preferred in casual conversations. Unfortunately, there are some exceptions, and ultimately you'll have to learn the usage of each verb from real examples.

Finally, the verb pairs you listed as examples are not really the same in meaning. I won't go into each example, but for 学ぶ vs 勉強する, see: Differences between 勉強する、習う、学ぶ and 学習する?

Answer 2

As a couple of your examples did not actually have identical meanings, I will focus on the one that better illustrates the nature of your question, namely 了解 vs. 分かる.

分かる is a general term for knowing something. It does not specifically imply full comprehension. 　

了解{りょうかい｝する is used with peers or people of lower status (corporate or social environments). Equivalent to saying ‘Roger’, ‘10-4’, or ‘Got it’. As 了解 is generally associated with military speech, it can be difficult to use it in most formal situations.

承知｛しょうち｝する means the same as 分かる, but is used with people who are above you in rank or status (customers, bosses).

かしこまりました means the same thing as 分かりました and is used in the same context as 承知しました. It is used as an affirmative that you have understood when addressing those of higher position.

理解｛りかい｝する is used to specify comprehension (full understanding).

As you can see, most of these have different meanings, nuances, or specific situations to be used in.

As an example of a 訓読み and 漢語｛かんご｝ which mean the same thing, take the following example:

保持｛ほじ｝ is an amalgamation of 保つ｛たもつ｝ (to keep; retain; maintain) and 持つ｛もつ｝ (to have, to hold). In English it would be ‘retain’ or ‘maintain’, usually used interchangeably with 保つ.

The reason that one or the other would be used is arbitrary, reflecting the environment that it is used in and/or the impression that the speaker wishes to convey. Aside from a simple literary inclination on the part of the speaker there is really no substantive difference in nuance.
漢語 usually sounds more educated, thus is preferred in academic surroundings. If used in casual situations, however, it might sound stiff and too formal.