Questions about example sentences with, and the definition and usage of "Defference"

A: Retain is to keep something you have already. Maintain is to support something so that it continues. So in your example he is keeping his position as the leader of the party

A: no difference.
In your example, He or she went to the United States in summer of 2017. When you say “last summer”, you are referring to the summer that happened last year.
If he or she said “I went to the United State this summer.”, he or she is referring to the summer of 2018.

A: but both are making same meaning

A: say = 말하다, 말을 입밖에 내다
tell = 말하다, 알려주다, 가르쳐 주다

A: They both mean the same thing, but "sufficently" is more formal than "enough." 何か質問がありますば質問に答えたいです。英語を勉強するがんばって！

A: Ought to is closer to advice, whereas have to is closer obligation.

Ought to = should
Have to = must

A: There isn't a difference. Both words are used to describe something in a positive manner.
'Aww yeah that goal was awesome!'
and
'Aww yeah that goal was amazing!'
mean exactly the same thing.

A: Increase is to add to in number or volume. Enhance is to add to in quality or become more detailed.
I increased the volume so it got louder.
I enhanced the image so it got clearer.

A: "confirm" is more like "verify". Sort of a "this seems to be true, but please make sure that it is actually true".

"check" is more like "looking to see something". So check a location to see if your missing item can be found there. Check outside to see if your friend has arrived yet. Check the weather to see what it is,. Check your email to see if there is anything new in there. Check the cookies to see if they are done yet, or if they need a few more minutes. Check to make sure you packed all of your things back into your bag before leaving class. etc.

So you might have to check a few things, to then confirm that something is true or finished or correct. But the "checking" part is looking for the information, and the "confirming" part is just the verifying that the information is correct.

So:

"check to see if it arrived" = go look to see if it is there
"confirm that it arrived" = go find proof that it arrived, go verify that it did actually arrive, go make sure that this fact is actually correct. "confirm" can also be used to talk about commitment, so "confirm your order before clicking submit" = doublecheck that everything is correct before completing the ordering process. Almost like a "I guarantee this is correct" = I confirm this is correct.

In your sentence, the meaning of "look" is probably the most appropriate, so use "check". Use "confirm" for other things like telling them to verify that the information is accurate, etc.

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Also, your sentence has a small error: it says "the" twice. "Check the the section A" But it using "the" here is awkward, so it would probably read better to say "Check section A" instead.

Also "to know what to be filled in this table" is a little awkward phrasing and unclear. At the very least, it is better to change it to "to know what NEEDS to be filled in this table." Or "to know what to fill in this table." or "to know how to fill in this table."

So:
"Check section A of document B to know how to fill in this table." This is best if [section A of document B] is a good reference or instructions.

"Check section A of document B to know what needs to be filled in this table." This is best if it is telling you to coordinate the information in section A of Document B with how this other table/form is filled out. So maybe it is two parts of a form, and they have to be filled out the same way, so it is trying to tell you to check how you filled out the earlier section and to coordinate it so that both sections match up correctly. So maybe the form has to be filled out differently for different purposes, so it is important that you keep the information consistent the whole way through it.

Just some suggestions.

A: Obvious is used in an absolute sense. If someone says "it's obvious he like her" there are most likely facts to back that statement up.
Apparent is less sure and most often used as an adverb (ie: apparently). Such as "apparently he likes her". Its a much less certain word.
Plain most often used with a sensing verb (ie: to see, to hear) and is close to obvious in certainty. For example, "it's plain to see that he likes her"

A: They all mean roughly the same with slight differences. “Explanation” gives a more general outline of what you want to know, while “Definition” is a specific and definite meaning of something. “Meaning” is the same as “definition” but it can be slightly more vague.

A: The difference between the two is that when you say "I might want to do that" and "I might as well do it" is that one implies that you're not sure if you're going to do it and the other implies that you are going to do it.

A: "Motherfucking" is used like "fucking." It's an adjective.
e.g. "That motherfucking car just cut me off!"

"Motherfucker" is an insult and a noun.
e.g. "That motherfucker just cut me off!"