Sterilize a jar or bottle or container with a lid (preferably glass) and dry completely.
Warm up oil...I use Jojoba, but you can use olive oil, or avocado oil or any organic plant based oil.
Do not boil it, just warm it.
Put crushed ginger, muddled lemon grass, bruised orange peel, etc. into your jar. Make sure they are dried with paper towels though...if they have water on them from washing they cause mold.
Pour the oil over the aromatics
Cover and store in SUNLIGHT.
Swish it daily.
After about a week, you have fragrance oil.

You can do so much with the oil. Make room freshener, hand lotion, body oil....so much. But if you want you can just use the oil in a tea light oil heater to fragrance the room.