Answer:
The soul is to the body what the astronaut is to the spacesuit. Take the astronaut out of the suit, and the suit's basically useless. Take the soul out of the body, and the body basically collapses. (Which is what death is - the separation of body and soul.)

A soul is Divine energy, a little piece of G-d within you. It is that part of you that exists beyond matter, beyond your body and your five senses. If you were blind, deaf, tongueless, noseless, and touch insensitive, you would still be alive inside yourself. But what part of you is still alive? That's the soul.

Simon Jacobson, author of Towards of Meaningful Life, explains the soul like this: "A soul is our inner identity, our raison d'être. Just like the 'soul' of a musical composition is the composer's vision that energizes and gives life to the notes played in a musical composition - the actual notes are like the body expressing the vision and feeling of the soul within them. Each soul is the expression of G-d's intent and vision in creating that particular being."

How do I express my soul?

To express your soul, you need to nourish your soul. A starving man cannot run a race, and a starving soul will find it very difficult to express itself.

Nothing is more nourishing for the soul than studying Torah. When you study Torah, you're reading G-d's mind, and when you're reading G-d's mind, your soul gets high, powering up with great gobs of spiritual energy, which it can then use to express itself by performing mitzvot.

What are "mitzvot"? Mitzvot are G-dly deeds - deeds with which G-d empowered our souls to express themselves and connect with Him. With certain mitzvot, we do not see a tangible, physical result (at least not immediately) - they're spiritual, so we can't see with our physical eyes the effect they have on ourselves and our world. But many mitzvot, while no less spiritual in essence, have the added benefit of a tangible, physical result - an improved relationship, and kinder society, a better world. The common denominator of all mitzvot is that they connect the person with his/her Creator and draw G-dliness into our world