A family of Microsoft word processing software products for creating web, email, and print documents.
Generally, Word online does not create a what-you-see-is-what-you-get type of view.
To see a true representation of the layout of your document, use the preview at File > Print. The preview actually makes use of PDF conversion.
In my experience, Word online remains a rather basic tool, to be used primarily when you make small changes in a document. You really need Word for a computer (PC or Mac) to do real work.