A helix is pretty much the same thing as a spiral. There are some mathematical differences between the two (for example, a spiral's diameter diminishes as it goes where a helix's stays the same, but for a layman, they are essentially the same shape.
I assume you are talking about this because of DNA. DNA is in the shape of a double helix, or two spiraling sides that are winding around one another.
If it's important to know the exact difference between a helix and a spiral, you can follow the link I've provided.
Helices are a 3 dimensional curves. It looks like a spiral or a spring. If you wound a thread along the curved surface of cylinder or a cone with common distance between the succesive wound of threads, the curved path of thread along the cylinder represents a helix. There is a central axis and raddius in the cylidrical helix remains constant, but in the conical spiral or helix the radius goes on increasing or diminishing successively. The the distance between the two succesive threads of the helix (also called the pitch of the spiral) remains the same.
In coordinate geometry we describe an equation of helix by:
x= a*sin(t), y= a*sin(t) and z = bt, which has has the radius
a and a pitch 2pib.
A helix in science and math is defined as a curve that has a tangent line that makes a constant line with a fixed line (axis). It is a spiral or curve in space. Examples of helix's are a spring such as one used to attach a trampoline to the side rail or a coil. To create a helix one could take a pencil and a piece of wire about the size of the pencil. Holding one end of the wire one should twist the wire around the pencil in a spiral motion. Once the wire is removed from the pencil it is in the shape of a helix. In biology the Helix model is used to demonstrate strands of DNA.