Assign a material to a particular object

Hello, I am pretty new to Blender and have a rather easy question, I am sure. I am doing a tutorial. I am making a tree. However, I have the material for the trunk and the material for the tree. When I choose a material, regardless of what is selected, it colors the tree AND the trunk. How can I resolve this problem?

Thanks, Colby.
Read this, it explains the whole process.
I use this process a lot :slight_smile: