Each chakra in a soul can connect with every other chakra in another soul. Life force is sent between the connected chakras. Usually, most of the life force goes between matching chakras — heart connects to heart, mind to mind, etc. Cross connections of chakras (e.g., will to heart) can lead to pathological situations. This topic is covered in more detail in Calculating Soul Connections.
The parts of the chakra that make the connection are in the set of aspects labeled outside the soul. These include inward ability, inward set point, inward intention, outward ability, outward set point, and outward intention.