The verb ''have''

First of all, I would like to say that I absolutely adore English language. The funny thing is that I like it much more than my first language, which is probably because my first language is very rare and I get most information from pages in English.
I also have a love-hate relationship with it, I tend to make many grammar errors with prepositions, time tenses, commas and have overall very clumsy sentences . At the end of the day though, I try really hard to write better.

My first question would be that what gives the perfect tense have to the sentence or to be more precise, to the meaning?
For example, there are two sentences, one is:
''No man before HAD dared to import a tea directly into Ireland.''
And the other one is: ''No man before dared to import a tea directly into Ireland.''

To a English speaker, this is going to sound extremely stupid, but I really can't see the difference. I have read many articles about the perfect tense and that the verb have adds the meaning possession but I just don't understand it.
So I would really appreciate it if someone would explain how the meaning changes with it because I can't figure it out.

I also read that the verb have puts emphasis on the action or the result, but I'm afraid it's not true (or if it's true then it's only one possibility of many), since it would be too easy.

Also I have been thinking about slight changes in meaning in the following sentences:
''I thought...'', ''I have thought...'', ''I have been thinking...''.
Correct me if I'm wrong (I am most definitely wrong), but in the first sentence it's one random thought, in the second sentence it indicates that I've been having that thought for some time now and the third one indicates that... Okay, now I'm confused. I understand that it's the progressive/ continuous tense, but again, I can't tell the difference between the last two.

Oh well... Again, I would be very grateful if someone would help me to understand the slight changes in meanings with this particular tense and if it's not too much asked then maybe fix some mistakes? Okay, it is too much since this post has probably too many mistakes...