This tutorial shows how to create a gradient pattern brush. The video also shows how to create double helix using this brush.
In this video tutorial, you will find instructions to create a circular logo in illustrator. To make this logo you need to use ellipse tool to create perfect circle.
This tutorial shows how to create a conical gradient in a few steps. To create an angular gradient please watch the video in this tutorial.
The tutorial shows how to apply a gradient fill to live text in illustrator. You can still edit text after making the gradient fill. Basically, In order to make the gradient, you should add fill color using appearance panel.