When your goat and harness are ready for work, that's when you are ready to train. Be patient, get someone to help you, and bring a lot of her favorite treats. Give yourself plenty of time. To start, your goat needs to learn a specific signal to begin moving. Tell her to "Walk!" using her name so she understands you're talking to her, and then tap her on the rump with your whip. Don't strike her, but tap her smartly so she feels it. The tap should come immediately after the voice command. As you give the command, have your helper lead her forward and give her a treat as she goes.
Have her walk a short ways, then pull on the reins and say "Woah!" Vary the lengths of your walk-woah cycles, and repeat them until your goat learns to start walking before your helper does. At this point she is probably also walking before you tap her with the whip. That's great! It means she's learned a voice command. From now on, you can only use your voice and a much lighter whip tap (more like a tickle), and only use the firm tap when she doesn't move off smartly from your voice. The purpose of starting out with a harder tap is to teach her to respect the whip and to have a reason to listen to your voice and move forward.
When she's walking from your voice, your helper can remove the leash and walk next to her. Your helper should also feed treats less often and begin to slowly drift away to the side or drop back so your goat isn't just following the cookies. This part will take a lot of time and patience. Break it up over several days or weeks, and expect some days to make loads of progress and other days to feel like you're back at square one. Try not to get frustrated. Goats are smart. While you are training her, she is also trying to train you!
I wrote an article a few years ago about proper harness adjustment and balance in the shafts
here. It might be helpful. Take your time and have fun with the process. It's important to keep in mind that if you're not having fun, neither is your goat and it's probably a good time to go back to something easy that she already knows and quit for the day. Always end every lesson on a good note, even if it's an easy one. Good luck!