There are some useful shaders here https://www.highend3d.com/maya/downloads/shaders/.

create a shaders folder and save them into there. You can then drag and drop them into the hypershade and they are ready to use for whatever you are modeling. To attach a shader to an object you can select the geomety and then right click on the shader and selcet assign material to selection.
In order to create your own shaders things get a bit more tricky as you need to learn how to add attributes to your chosen shader and will then need to tweak these to get the desired look.
For the texturing process you need to learn how to lay out the uvs for the item you are texturing. Once this is done you select the uv snapshot option under the polygons tab in the uv texture editor. You then add texture over the areas of the uv map where you want it to be. Once complete you simply assign it to the appropriate part of your shader, bump, colour, specular etc.

Also laying out uvs can be a bit of a nightmare task and I found this plugin to be a great help with getting the job done.

https://www.pullin-shapes.co.uk/page8.htm


Hope all this helps and good luck,

Leon