I use them for:
Magick, Chakra work, Mediation
Stress-management and relief
Concentration and Focus
There are probably a million and one other ways I could be using them on top of those.
But I wanted to write a quick introductory post because I will likely be coming back to this theme again and again. Scent can be a vital and deeply pleasurable part of ritual work and essential oils can induce a far larger range of moods and associations than other options such as incense. They can also be a discreet way of practising low-key magick in the workplace or other areas of life where you do not want or need to draw a huge amount of attention to your practise.
A few words of warning which are oft repeated in the various books:
1. Check the contraindications before you use the oils - some should be avoided by pregnant women, people with allergies or will irritate the skin if applied directly.
2. Don't use them internally.
3. Always check you are buying "pure essential oil" (a good way to tell is price - if they seem so cheap it is too good to be true - they are probably not pure).
My top aromatherapy books for inspiration and information are:
The Fragrant Pharmacy by Valerie Ann Worwood
The Encyclopedia of Essential Oils by Julia Lawless
So dive right in to a wonderful, scented second half of the year!