Zotero's Feeds feature allows you to subscribe to updates from all of your journals and add relevant articles to your Zotero library.
To begin, you first need to find the RSS feed addresses for the journals that you'd like to follow. This can be done in a few different ways:
You'll now see your Feeds appear in the collections pane under My Library and Group Libraries (if you have previously created any group libraries).
You can browse your journals individually. Journal titles in bold have unread items; articles in bold have not been viewed. To add an article to your library, select in the middle pane and select Add to "My Library" in the top right. Note that the item metadata will usually require some tidying up, as the metadata coming from the RSS feed is frequently incomplete or improperly coded.