Word can automatically number the captions for tables, figures, and equations.
The following video will show you how to insert objects. Although it refers to "Word 2010", all of the information remains correct today.
Right-click the object you wish to caption and select Insert Caption… from the shortcut menu. For tables, right-click the crosshair icon that appears at the top-left corner of the table when your cursor is anywhere on top of it.
In the Caption dialog box, select the label that applies to the object you have selected (e.g. “Figure” or “Table”) and select the positioning of the caption (e.g. above or below the object).
Type your text in the Caption: box. (This field has a 250-character limit, so if your caption is longer than that, you can refrain from adding it here, and instead add it after you've inserted the caption -- Step 6)
As long as you have already set up your Heading 1 style to provide the chapter number (see Automatic Chapter and Subsection Numbering), you can include that chapter number in your caption number (e.g. “Figure 3-2” or “Table 2.1”). This is the only way Word understands where each chapter starts; otherwise, you will get an error. If you’ve done that, then in the Caption dialog box,
Click the Numbering… button and check the Include Chapter Number box.
Select the separator you wish to have between your chapter number and the caption number and click OK.
Click OK to exit the dialog box.
If you waited to enter your caption text (Step 3), now you can type it in.
All the captions in your document are styled with the Caption style. If you do not like the format of your caption text, do not edit them one-by-one, but modify the style instead (see Working with Styles for more details). That said, if you want your label & number to be bold and the caption text to be regular (e.g. "Figure 2.1: This is my caption"), then you will have to set the label & number to bold yourself -- Word can't mix font settings within a caption, unfortunately.
Word will renumber your captions appropriately if you insert a new figure before other figures in your document.