There are two main methods of using essential oils:
 

TOPICALLY: through the skin, AROMATICALLY: through inhalation

Although organic and therapeutic grade essential oils are natural and generally safe to use, always practice essential oil safety by doing your own research. You are still likely find conflicting advice about how best to use an oil; for example, some practitioners adamantly oppose any form of neat application (using an essential oil without first diluting it in a carrier oil such as fractionated coconut oil) whilst others are happy to advocate for it. In these circumstances, it is important to trust your own intuitive sense about how you wish to use a particular oil.  Occasionally I use some oils without diluting them (such as lavender on a cut or burn), but that is rare. 

Essential oils are not less effective if diluted in a carrier.

When using essential oils on children, young people under the age of puberty, and the elderly, always dilute the oils in a carrier first. As a rough guide, I would generally not recommend using essential oils on children under the age of 3, for children between 3-6, use 1 drop of essential in 10ml of carrier oil, and for children over 6, use 2 drops of essential oil in 10ml of carrier oil. There are many helpful resources online, but as with any information, exercise your own caution and discernment before following any advice found online.

There are some oils which should not be used on pregnant women and babies, so be sure to do your own research or consult a qualified aromatherapist before using any oils whilst pregnant or on babies.