I think whatever resource you used to learn the rules wasn't clear because you have the wrong idea about how liberties work. Try this site:

http://playgo.to/iwtg/en/

Okay i understood that now, but I still have this one question:

http://playgo.to/iwtg/en/count.html

Here its says that the first board is considered finished, because the black stone, as pictured in the second board would be captured quite quickly. But even if so, wouldn't it shrink down white's territory drastically? Because as he said, stones are not counted as points, so white would be forced to place some stones in its own territory, reducing his points a lot. Do I oversee something here?

What he should have said is that the Black stone could be killed, not that it could be captured. In the second diagram the lone Black stone is dead, and after the players have agreed to end the game it is removed without capturing. OC, that means that Black has to agree that the stone is dead.

There are ways of dealing with disagreement, but since you are playing beginner vs. beginner, the easy way is to play by area scoring, which counts both stones and territory, but does not count prisoners. Then White can capture the Black stone, and the score remains the same. White wins by 5 points.

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

But why would Black disagree with the stone being dead if he could win points, and make a difference on how the end result will be, in some cases maybe even deciding who wins?

You need to read up on the difference between Chinese and Japanese scoring. Under Chinese scoring your concerns do not come into play, as the score is not affected. Under Japanese scoring it is, but there is a provision in the rules to back out effects of disputes: the problem, of course, is that beginners may not back out accurately. But the bottom line is that, if played correctly, disputes as you mention do not affect the end result.

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Still officially AGA 5d but I play so irregularly these days that I am probably only 3d or 4d over the board (but hopefully still 5d in terms of knowledge, theory and the ability to contribute).

think of it as a shortcut.

if the black stone cannot prevent itself from being surrounded/suffocated, then we are just saving ourselves the time and energy of actually surrounding/suffocating it and capturing it.

As Bill says, if we were to use Chinese rules, then the score wouldn't change whether you played it out or not.

Using Japanese rules, if we were to force white to capture the stone without black having to respond, then white would lose points. But at this point, its both courteous and a shortcut -- black can't live, so its considered dead. There's no point in playing it out.

You mean why would he agree? The point is that disagreeing would not make any difference in the score. Different versions of territory rules handle the disagreement differently, but they agree with each other except in rare instances. They certainly agree here. The lone Black stone is dead. You can learn such methods if you like, but the easy thing to do is to use area scoring.

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

... And this long series of discussions is why I think we should just abandon territory scoring entirely. Why do we make this so hard on ourselves?

In any case, as Bill said, use area scoring, a point for each stone on the board, and a point for each empty space. If one side disagrees, resume play.

_________________
Tactics yes, Tact no...

And no more bent 4 controversies.