People use these words in a lot of different ways, often overlapping.
To make the most common distinctions, though, people use the word “soul” to refer to the aspect of the self that retains the emotional memories and deep understandings that define the unique person that each of us is.
The word “spirit” is used to describe an abstract quality of being that is present in all life forms, coming from a Greek word that also means “breath:” hence the words inspiration and respiration. To die is to “expire,” or “give up the ghost,” which is another word used interchangeably with “spirit.” To be energized or excited is sometimes referred to as being “spirited” and athletic departments often have “spirit teams” to help build that kind of energy. In contrast, to be “dispirited” is to lack interest or energy.
“Spirit” with a capital S is generally used as an alternative to the word “God.” It’s referring to the Nurturing Source of All That Is, and is sometimes personalized in the same way as “God,” “Mother God,” “Father,” and “Father God.” The usual assumption is that our individual spirit is a function of our relationship with the greater Spirit.
Holy Spirit is a term that emerged in Christian theology as the means by which the Creator God enthroned outside of the created world can communicate with, be in communion with, and affect the beings who populate this world. It’s the active aspect of the Trinity; the part of the one God that we can relate to, what Jesus called “the Comforter.”