Dew point in basement
The &quot;dew point&quot; is that combination of temperature and humidity where dew starts to form.  It does this because the lower the temperature of the air the less humidity is can hold.
In your case you measured a temperature of 17C and 70% RH, as long as your temperature stays above the dew point no liquid will condense out.  You will note that as the temperature decreases the RH will rise until it reaches 100% at the dew point.  Now the air is 100% saturated with water and any additional reduction of temperature will force water out of the air.
The question of where is difficult to predict.  It usually doesn't &quot;rain&quot; in a home or basement so wherever the coldest spot is, like your concrete wall or a metal post is where you will see the water first.  If the temperature continues dropping more and more water will condense out.

Does this mean if I bring in the basement an object which has lower
than 11°C, the condense will start to show up around this object?

Probably.  If the object cools the air around it to below 11C it may condense or even freeze onto the surface of the object.

Does this mean if my walls would have 11°C the water would start to
create on them?

Almost certainly!

I can not understand how we can cool the air temperature to 11°C if we
have 17°C degrees. Then the temperature would no longer be 17°C, but
11C and if it would have 11, then the dew point would have a different
value. I really don't get the concept. Thanks.

The dew point doesn't change until the amount of water in the air changes.  Part of the problem in a home is that the moisture content as well as the temperature are dynamic.  Generally you want to avoid conditions that approach the dew point so that you don't get moisture damage, mildew, mold, etc.