Can I open a word document forom the cloud in Pages if I don't have word installed on my new Mac air

Yes. Pages on Mac will open Word documents just fine, the Word app is not required at all. It will convert them into a Pages document, and you will need to export back out to a Word document if you wish to retain that file format.

Do note, some differences in layout and formatting may occur during the translation process from Word to Pages and then from Pages to Word.