Can't understand なら usage in this context


So I'm reading Genki II where they introduce なら. There's a dialogue which has
the following context: a guy asks his female friend Kyouko to cover for him at
work (he's an English teacher). The friend is hesitant and says:

  * 私、英語を教えたことがないし、できない。 to which the guy answers:
  * 大丈夫だよ。ぼくより英語が上手だし、きょうこさん **なら出来るよ** 。

What is the literal meaning of this? "You're better at English than I am, so
if it's you, you can"? This makes literally zero sense. So I _suspect_ it
actually has the meaning of "If there's someone who can do it, it's you" but
even if my assumption is correct, I still can't see how なら logically fits into
this.

Then there's also another dialogue example. Context: a guy and a girl are in a
fitness store. They see a fitness machine and are discussing it:

Guy: このフィットネスマシンはどうですか。

Girl: 便利そうですね。

Guy: ええ、このマシン **なら** 、家で運動できますよ。

I've read all I could find on the Internet about なら and while some examples
make sense, I still don't understand it in actual, unadapted real-life
sentences, even as simple as these ones. What does it mean in the above
dialogue? "If it's this machine, you can use it at home"? Surely that's not
correct.

Thanks in advance.




They like to teach なら as "if", but just like all the other words corresponding
to "if" in Japanese, in reality this actually has a "when A then B" kind of
meaning, which is broader than a simple "if A then B".

In your first example, what the second sentence really means is:

  * "Don't worry! Your English is much better than mine, so **for you** it should be a piece of cake."

Here なら is used to mark Kyoko as a possible candidate for the action of
teaching English, and then say what would happen if she, of all people, did
that. The implied suggestion is that if it were the speaker, he would do a
pretty poor job.

Similarly, in the second example なら comments on this machine as opposed to
other possible machines, with which it wouldn't be possible to work out at
home:

  * "Yes, when you have this machine you can work out at home".

The reason なら is used here is because there is an idea of choice: you're
saying what would happen if one choice were made, and implying that with other
choices some else would happen.

AならB is best thought of not as "if A, then B", but as "under the assumption
that A has become a reality, B". It's commonly used for making some sort of
assumption, in contrast to other alternatives.




They like to teach なら as "if", but just like all the other words corresponding
to "if" in Japanese, in reality this actually has a "when A then B" kind of
meaning, which is broader than a simple "if A then B".

In your first example, what the second sentence really means is:

  * "Don't worry! Your English is much better than mine, so **for you** it should be a piece of cake."

Here なら is used to mark Kyoko as a possible candidate for the action of
teaching English, and then say what would happen if she, of all people, did
that. The implied suggestion is that if it were the speaker, he would do a
pretty poor job.

Similarly, in the second example なら comments on this machine as opposed to
other possible machines, with which it wouldn't be possible to work out at
home:

  * "Yes, when you have this machine you can work out at home".

The reason なら is used here is because there is an idea of choice: you're
saying what would happen if one choice were made, and implying that with other
choices some else would happen.

AならB is best thought of not as "if A, then B", but as "under the assumption
that A has become a reality, B". It's commonly used for making some sort of
assumption, in contrast to other alternatives.

