All you'll need for this tutorial is a colour scheme.
Firstly, select the Gradient Tool then select the gradient option at the top of the screen (as shown below).
This screen should appear. Click on the first gradient colour to open the colour selector menu and select your first colour from your colour scheme.
Click to the right of the first colour to create a second colour. Click the second colour and select the second colour from your colour scheme.
Click to the right of the second colour to create a third colour. Click the third colour and select the third colour from your colour scheme.
Click on the final colour to select your fourth colour.
Give your gradient a name (if desired). Then press OK.