I want to dye just the underneath part of my hair a darker color, but am not sure if I just separate a line from ear to ear or what?? PLEASE HELP!

If you want to dye the lower layer of your bangs, to create more of a "layered" effect, pick up a do it at home box from the store (garnier or loreal works fine). Make sure you get a dye that is permanent.
Now, before you apply the dye, you are going to want your bangs to be layered. If doing it yourself, texture the top and piece it out, adding asymetry is always fun (think Sassoon). Next, separate your bangs, approximately from your temples (if you go ear to ear, it won't create the right effect, you want to keep this centered, to draw the viewer to your face). Clip the top back, apply the dye (Note: Make sure the dye is only a few shades darker than your hair colour) wait, rinse, and dry. Afterwards you may want to retouch and texturize your hair more, thinning the top layer so that the darker, intense colour shows through.

Cheers-

-m

I reread your question... did you want the front darker, or the back?

Just the underneath part of my hair, the hair that lies closest to my neck and leave the top layers the natural light brown that they are, and the underneath a dark brown, to show contrast... because I have really fine/thin hair

If you are doing the back, pull your hair up, as if you are pulling it into a ponytail. Then, let the bottom half slip out from your thumbs. The hair that falls out is the portion you should dye. Again, you may want to get is cut before or afterwards, so that it is more textured, otherwise, the color may not show through as well.

Maemab, I've answered a similar question to yours. Please refer to this link.

https://www.askmehelpdesk.com/beauty...own-27621.html