I think you've answered your own question here! You want to know how to lay in bed together and start things off, but your best friend is helping you to find yourself and your sexuality. Maybe she can guide you through it!
It's important that you are relaxed and comfortable with the person that you want to start experimenting with. If your best friend has already said that she will help you, it sounds like you're pretty comfortable with her already and you trust her. This is vital - make sure you talk about everything that you feel you want to talk about.
Go with your instinct
It's pretty likely that once your best friend helps you to start things off, it'll start coming naturally. Think about what you like - she could like it too, and if she doesn't - that's why you go back to the talking thing I was just mentioning above.
You might also want to talk to some other people that you trust who will not judge you and will understand you. But if they have questions, you might want to watch this video by Scarlet Saint so you can help to bust some common misconceptions about bisexuality:
Hope this helps!