Briefly described:
1) In the configuration menu you define the "sidebar", for example you there insert wiki:sidebar
2)Navigate to the wiki:sidebar (brother or index, etc.) and edit this page. Perhaps dokuwiki tells you that it is not present yet.
3) Fill this sidebar-page with your requirements, so that it looks like this:
__**NEWS 2017**__
* [[news:2017_01_06|News I 2017]]
* [[news:2017_01_06|News II 2017]]
__**NEWS 2018**__
* [[news:2018_01_06|News I 2018]]
* [[news:2018_01_06|News II 2018]]
* etc.
Consider the two or four blanks at the beginning of each line"
Change the links to your requirements!
The __ underscores make the text being underlined.
The ** asterisks make the text being bold.
4) Save the page. Now your sidebar should appear, if your template supports this.
5) Also consider making use of indexmenu, etc., if your navigation menu gets bigger and bigger and you want to get it automatically.