How to use essential oils?

I just got three bottles of essential oil for aromatherapy (therapist recommended for anxiety and depression). Two blends and lavender oil.  I was going to just put it on my wrists, but apparently you aren't supposed to put it directly onto skin? How should I apply it? I'm going to be using them a lot at school so I'd like it to last a good 7-8 hours, if possible. I do have argan oil if I need a carrier oil, if it works for it. How do I use it? Thanks for any advice! ^^