The Holy Spirit is the third part of the trinity and it is the hardest to under stand. In the apostles creed they refer to the Holy Spirit as the Holy Ghost because he is not human like Jesus but he is in are spirit and he lives in us and he is the fire burning in side of us. The Holy Spirit where the tongues of fire on peoples head at pentacost. Also the Holy Spirit is are soul in side of us and he is the one that leads us and guides us through are faith journey. The Holy Spirit is kind like Gods brother and Jesus is Gods sons I think it the trinity as a apple like the core is God and fruit is Jesus and the skin is the holy spirit that is how I remember the trinity.