How can I find out, how the recipients reacted on the campaign?

You can find this information in the report of each campaign. Go to reports and open the details of campaign. The button Activity shows you all information about who are the Openers, Clickers, Bounces etc. Keep in mind that this information is only visible in Standard an Pro package.

As alternativ you can find this information under "Contacts" --> "Active Contacts". Click on "Advanced search" and set your search criteria. "Email" is a preset criteria, but you can change this to a behavioral attribute by selecting from the drop-down, e.g. "has clicked". From the second drop-down you can then select the relevant newsletter. 

TIP: You can also add additional criteria to run a more complex search. 

Once you have set the search criteria, click "search". The relevant contacts will be shown under the search field.