There is the TagBundle in SuluCMF included. I know how I get the Tags for a given item.
How can i get relates articles for this item in SuluCMF the best way?
Depends on what you exactly understand under related articles. A simple solution would be to use the SmartContent. Then the content manager can use the smart content to filter the pages by tags.
Another solution would be to use the internal links content type, so the content manager can choose manually which pages are related. This will of course be more work for the content manager, but the results would be the most accurate.
If you really want to filter based on the tags you assigned to the page, which should show the related elements, then you have to implement something on your own, since we are not supporting something like that out of the box. The DocumentManager::createQuery method might be useful for that.