how to open word documents

I'd recommend you ReaddleDocs or GoodReader. For editing DocsToGo or perfect CloudOn.

CloudOn is only for iPad!

The most usable app for opening Word docs is definitely Pages. It is made by Apple and is $10.

If you simply need to view (and not edit) a Word doc, you can simply email it to yourself. Open the email on your iPhone and tap on the attachment and you will be able to see your document.