Google Scholar's My Library feature allows you to save articles directly from the search results page, organize them by topic, and search the full-text from within your library. You can easily export your citations to a citation manager like Zotero or Mendeley.
In order to use My Library and other personalized features of Google Scholar, you will need to create a Google account. You can do so here.
After you've created your Google account and logged into Google Scholar, you can access My Library by selecting "My Library" in the upper left corner of the Google Scholar homepage.
You can organize your library by using Labels.