how do i set margins in word 2016?

Look at the left end of the Layout tab of the ribbon:

You should be aware, though, that "margins" (and most of the other items in the Page Setup group) affect the entire section to which they're applied. If you want to change the appearance of just one or a few paragraphs, the settings you need are the left and right indents in the Paragraph dialog:

Page margins:

• Activate the Layout tab of the ribbon.
• Either click the Margins dropdown in the Page Setup group, and then select an option, or
• Click the little arrow in the lower right corner of the Page Setup group to activate the Page Setup dialog, then set the margins in the Margins tab.

Paragraph indents:

• Activate the Home tab of the ribbon.
• Click the little arrow in the lower right corner of the Paragraph group to activate the Paragraph group.
• Set the indents in the Indents and Spacing tab.