These instructions will only be necessary if you are using the Basic skin provided by the Lindens. (If you have purchased a custom skin, your eyebrows will probably be painted onto your skin.)
When you put on your new hair, you'll find that you no longer have any eyebrows or facial hair. This is because the Lindens, for whatever reason, chose to link the color of the head and facial hair. (There is only one hair-color slider, and it changes both.)
In order to see the texture of your new hair, I have set the color to White. (Color is provided by the texture itself, not the sliders.) This, of course, also makes your eyebrows and facial hair (if any) white; so I have chosen to eliminate them, and included colored eyebrows in the hair package, to replace them.
1. Wear your new hair, right-click on your Avatar, and enter Appearances.
2. Click on the Skin tab, then on Skin Color to choose that pane.
3. Open your inventory, and locate the Eyebrows in your Hair Package.
4. Arrange the screen so you can see both your inventory and the Appearances dialog, and drag the desired eyebrows into the top well of the Skin Color Texture bar. (It's labeled Head Tattoo.)
5. Let go, and you'll find that your new eyebrows are showing on your avatar.
6. If desired, click on the Hair tab, choose the Eyebrows pane, and move the sliders to change the height, arc, etc. of your eyebrows.
7. Save your new skin, and exit Appearances.
And that's all there is to it!
Hope this helps!
If you would like to see the other tutorials in this series, click here.