user11283: Today, we are living in very complex world. Various lifestyles inspire us greatly. So as being a modern layperson, it is difficult to know good karma and bad one. How would I will be on good path and eventually attain Nirvana with 21 century lifestyle? I wouldn't know which activities and deeds have to stop from doing. Which Buddha teachings do I have to follow, differentiating current lifestyles and livings?

user471: Virtue or sila at the very minimum is the five precepts. This is the minimum practice of Buddhism.
The five precepts (and other precepts) are undertaken as a training on a "try your best basis". If you lapse, you should try harder next time, without feeling remorse. Striving for perfection in the practice of virtue or sila is not required for lay persons.
Further practice of virtue is by the eight precepts (usually in the context of uposatha), ten precepts (as a novice monk), Right Livelihood, Right Speech and Right Action.
Right Livelihood for laypersons is explained in AN 5.177.
Further information can be found in AccessToInsight's virtue (sila) page, including sutta verses.
To practice virtue (sila), the first step is to vow to undertake the training of the five precepts, and then practice them with heedfulness (appamada).
The second step is to adopt this thinking from AN 5.57:

“And for the sake of what benefit should a woman or a man, a
householder or one gone forth, often reflect thus: ‘I am the owner of
my kamma, the heir of my kamma; I have kamma as my origin, kamma as my
relative, kamma as my resort; I will be the heir of whatever kamma,
good or bad, that I do’? People engage in misconduct by body, speech,
and mind. But when one often reflects upon this theme, such misconduct
is either completely abandoned or diminished. It is for the sake of
this benefit that a woman or a man, a householder or one gone forth,
should often reflect thus: ‘I am the owner of my kamma, the heir of my
kamma; I have kamma as my origin, kamma as my relative, kamma as my
resort; I will be the heir of whatever kamma, good or bad, that I do.’

The third step is to understand more deeply from the Dhamma on Right Livelihood, Right Speech and Right Action, and practise them with heedfulness (appamada).
Also, please see this answer for the question "Are the Five Precepts a gradual training?".

11283: <p>Today, we are living in very complex world. Various lifestyles inspire us greatly. So as being a modern layperson, it is difficult to know good karma and bad one. How would I will be on good path and eventually attain Nirvana with 21 century lifestyle? I wouldn't know which activities and deeds have to stop from doing. Which Buddha teachings do I have to follow, differentiating current lifestyles and livings?</p>
 471: <p>Virtue or <em>sila</em> at the very minimum is the <a href="https://www.accesstoinsight.org/ptf/dhamma/sila/pancasila.html" rel="nofollow noreferrer">five precepts</a>. This is the minimum practice of Buddhism.</p>
<p>The five precepts (and other precepts) are undertaken as a training on a &quot;try your best basis&quot;. If you lapse, you should try harder next time, without feeling remorse. Striving for perfection in the practice of virtue or <em>sila</em> is not required for lay persons.</p>
<p>Further practice of virtue is by the <a href="https://www.accesstoinsight.org/ptf/dhamma/sila/atthasila.html" rel="nofollow noreferrer">eight precepts</a> (usually in the context of <em><a href="https://en.wikipedia.org/wiki/Uposatha" rel="nofollow noreferrer">uposatha</a></em>), <a href="https://www.accesstoinsight.org/ptf/dhamma/sila/dasasila.html" rel="nofollow noreferrer">ten precepts</a> (as a <a href="https://en.wikipedia.org/wiki/Samanera" rel="nofollow noreferrer">novice monk</a>), <a href="https://www.accesstoinsight.org/ptf/dhamma/sacca/sacca4/samma-ajivo/index.html" rel="nofollow noreferrer">Right Livelihood</a>, <a href="https://www.accesstoinsight.org/ptf/dhamma/sacca/sacca4/samma-vaca/index.html" rel="nofollow noreferrer">Right Speech</a> and <a href="https://www.accesstoinsight.org/ptf/dhamma/sacca/sacca4/samma-kammanto/index.html" rel="nofollow noreferrer">Right Action</a>.</p>
<p>Right Livelihood for laypersons is explained in <a href="https://suttacentral.net/an5.177/en/sujato" rel="nofollow noreferrer">AN 5.177</a>.</p>
<p>Further information can be found in <a href="https://www.accesstoinsight.org/ptf/dhamma/sila/index.html" rel="nofollow noreferrer">AccessToInsight's virtue (sila) page</a>, including sutta verses.</p>
<p>To practice virtue (sila), the first step is to vow to undertake the training of the <a href="https://www.accesstoinsight.org/ptf/dhamma/sila/pancasila.html" rel="nofollow noreferrer">five precepts</a>, and then practice them with <a href="https://buddhism.stackexchange.com/q/22181/471">heedfulness (appamada)</a>.</p>
<p>The second step is to adopt this thinking from <a href="https://suttacentral.net/an5.57/en/bodhi" rel="nofollow noreferrer">AN 5.57</a>:</p>
<blockquote>
<p>“And for the sake of what benefit should a woman or a man, a
householder or one gone forth, often reflect thus: ‘I am the owner of
my kamma, the heir of my kamma; I have kamma as my origin, kamma as my
relative, kamma as my resort; I will be the heir of whatever kamma,
good or bad, that I do’? People engage in misconduct by body, speech,
and mind. <strong>But when one often reflects upon this theme, such misconduct
is either completely abandoned or diminished</strong>. It is for the sake of
this benefit that a woman or a man, a householder or one gone forth,
should often reflect thus: ‘I am the owner of my kamma, the heir of my
kamma; I have kamma as my origin, kamma as my relative, kamma as my
resort; I will be the heir of whatever kamma, good or bad, that I do.’</p>
</blockquote>
<p>The third step is to understand more deeply from the Dhamma on <a href="https://www.accesstoinsight.org/ptf/dhamma/sacca/sacca4/samma-ajivo/index.html" rel="nofollow noreferrer">Right Livelihood</a>, <a href="https://www.accesstoinsight.org/ptf/dhamma/sacca/sacca4/samma-vaca/index.html" rel="nofollow noreferrer">Right Speech</a> and <a href="https://www.accesstoinsight.org/ptf/dhamma/sacca/sacca4/samma-kammanto/index.html" rel="nofollow noreferrer">Right Action</a>, and practise them with <a href="https://buddhism.stackexchange.com/q/22181/471">heedfulness (<em>appamada</em>)</a>.</p>
<p>Also, please see <a href="https://buddhism.stackexchange.com/a/45296/471">this answer</a> for the question &quot;Are the Five Precepts a gradual training?&quot;.</p>
