Healers are unique characters that are found in most cities within the game. For a fee, they will fully restore your partys HP. For Kharg, these are women in a nurses hat; and for Darc they are blue Quorops (these are the Deimos that look like frogs) with white hats.
Your first opportunity to earn this is in Khargs first chapter. A healer is located in the lower left hand corner of the bar in Yewbell (the bar is the closest enter-able building to the exit on the right). She will charge you 10G for her services. This is often a better option to healing your party early on than using Paulettes skill, as that uses precious spiritual stones which are a little hard to afford early on.