There are some spam issues in the comments, so I had to disable comment editing for a short time. It'll be back once the spam bots are gone. FYI... they leave a comment with "great" and then edit in the spam stuff later, to get around the filter.
(Like all "setzen"-versions, it needs a direct object, so if you talk about a person sitting down "here", you'll need to use it reflexively "sich+Acc hersetzen". The core idea is sitting down "here" as opposed to "over there".)