New to blender. Trying to position textures correctly on a mesh I have a mesh (a person) with different materials assigned to different parts. I have a png file of an eye iris. I have each eye on the model assigned with a different material so I can make sure I can position each one properly. Can someone help me figure out how to attach the file as a texture to the material and position it correctly on the eye? It keeps coming out out warped and twisted.
A bit hard to know without a screenshot, but here are my 2 cents:

Assuming you have already correctly unwraped the eye UV map, you need to add an Image Texture node to your shader with the Texture Coordinate and Mapping nodes, like so: 



On the Image Texture node, add your texture by clicking on the Open button.