Depending on your status, you may have to charge VAT.
Turning taxes on
Under Settings → General, tick « enable taxes ». A Tax tab appears, where you set your rates (20% in France, for example) and choose how prices are displayed — tax included is the usual choice for consumers.
Prices with or without tax?
When you sell to consumers, display prices tax included. For B2B, prices excluding tax are more common.
Be careful: tax rules depend on your own situation. If in doubt, have an accountant check your setup.