Hi NoVoice,
I use them in an oil burner almost everyday wafting through my living areas.

I used to own a whole kit that was a gift. Came in a beautiful wooden box, filled with different essential oils and a chart for specific uses. I use them for stress mostly

These days I tend to just use a lavender or a jasmine oil. Sometimes mixed. Sometimes I'll put a few drops of eucalyptus oil.

You can find charts online if you're looking for specific oils and uses.

edited to add: I try to buy really good quality ones when they come on sale.
I have bought certain types of lavender for example that just wasn't up to standard.