Hey I am new to Maya and have the student version of Maya 2017. I did some modelling and I think I am going in the right direction

My problem now is that I still need tutorials to do things but most tutorials refer to Maya 2016 or older. This isnt a problem in the modelling stage but when it comes to texturing they use mental ray which is not supported by Maya 2017 and therefore I can never finish my work

So I have a couple of questions, please excuse me if they are stupid but like I said I am new

1) What are HDRI images? How do I use them? What can they do? Where do I get them?

2) What is an alternative for mental ray's standard textures? Maya 2017 does not seem to have that sophisticated textures premade like chromium or other materials.

3) How can I create realistic and good looking textures with the hypershade? So far all I get are blinn plastic looking things or lambert dull plastic looking things I would especially appreciate advice on wooden textures, chromium, metal and other basic materials

4) What is arnold? What can it do?

5) Which renderer should I use? Maya Software, Arnold,....

Thank you for your answers (well if there are any)