How can I hide part of a caption in the document but show it in the contents?

You'll need to use field codes. For each figure, you can position the cursor at the end of the caption line, and press Ctrl+F9 to insert a field. Between the braces ({ }), type TC "Figure followed by a space. Next press Ctrl+F9 to insert a new field inside the first field. Between the new braces, type SEQ Figure \* ARABIC \c. This will grab the figure number that Word autogenerated for the caption. Now, after the closing brace for the SEQ field, press Tab (since your screen shot shows that you want the figure number and the caption text to be separated by a tab space), and type the caption text as you want it to appear in the Table of figures. Finally, type " \f F \l "1". For example, if I want the caption that appears below the figure to say 'The xxx menu,' but the Table of figure to show 'The xxx menu in the yyy program,' I would use this:

{ TC "Figure { SEQ Figure \* ARABIC \c } The xxx menu in the yyy program" \f F \l "1"}

Do this for every captioned figure in your document. (You can copy and paste the entire TC field, including the braces, and then change just the text that should appear in the Table of figures. All the numbering will be corrected when you update field codes later.)

Then, position the cursor in the location where you want the Table of figures to appear, and press Ctrl+F9 to insert a field. Between the braces, type TOC \f F \h \z.

Press Ctrl+A to select the whole document, and then press F9 to update all field codes.

Here's the Table of figures that I ended up with after adding a caption and TC field to another figure in my document.

And actually, if you want the chapter number prefixed to the figure number, with a period as the delimiter, as your screen shot shows, you'll need to add another field before the SEQ field (Ctrl+F9), and type STYLEREF 1 \s between the braces. Then, between the closing brace for the STYLEREF field and the opening brace of the SEQ field, type a period. For example:

{ TC "Figure { STYLEREF 1 \s }.{ SEQ Figure \* ARABIC \c } The xxx menu in the yyy program" \f F \l "1"}