1. What is Spirit? God energy that imbues all living and non-living things. God is thought in action. God is thought that manifests as form in accordance with the Law of Cause and Effect. We are each unique, individual expressions of God. It's our true nature...the part of us that never dies, that is eternal, infinite and limitless. It's in everyone one of us. Call it your "Soul", "Higher Self", "Christ Self", or whatever. It also gives life to our otherwise inanimate bodies. Spiritual things are only invisible to those who haven't raised their consciousness to Spirit.
2. What does it do? Spirit doesn't have to "do", but can also only "be". It all depends on what level of consciousness you are at and the world/plane you are reincarnated in. Spirit can be used to create form. Think of philosophy 101...Homer's Socrates...what is a table? Its an idea that has taken on form. Without the idea there can be no form. Thought (the idea) always proceeds the form. Thus we can create or change our own realities with our thoughts and emotions using just the seven basic tools of Meditation, Affirmations, Affirmative Prayer, Visualizations, Contemplation, Journaling, and Goal Setting – Planning. There are many other tools such as chanting, channeling, re-birthing, Neuro-Linguistic Programming, etc.
3. It is your job in this life to awaken to your spirit (which is already whole, complete and perfect), raise your consciousness to your divinity, enjoy life, and manifest as form your God-given gifts and talents (latent thoughts within you). To do otherwise would be "sin” which is that which separates us from God/Spirit/Goddess/All-That-There Is.
4. Seek spiritual knowledge, have faith/conviction in it, and raise your consciousness. You will automatically reap the benefits of God, to include love and joy, peace, health, abundance, prosperity, etc. We all, being part of the same One, will reap the benefits. Thus, our goal in life is to know, love and serve God.