Here are the steps:
You can use the Zotero Connector extension on Chrome to directly import references from PubMed.
Simply, do a search as per normal and on your selected article page click on the Zotero icon in your Chrome browser. You will then be asked to select which references you'd like to save to your Zotero Library.
You can create a reference manually by using the 'New Item' button.
While there are many fields, you need only populate the fields that are essential to the citation. Auto save option adds the reference to the Zotero library.