@petrescatraian Have a look at /help/user/channels – the channels are explained there.
As for your settings, I’d change the following.
Clear the settings under Full Text Search, as that field normally uses MariaDB’s “boolean mode” operators. For example: +(tag:hashtag,tag:hashtag1,tag:hashtag2)

Under Languages, it looks like you’ve only selected ‘Unspecified’, which means that only posts for which no language information has been detected will be displayed (e.g. posts that contain only an image or too little text to determine the language with certainty). If you want to see all languages, you need to select all items in the list.