Were do I start with unity5?

My recommendation would be to start by reading through the Unity Manual. You don't need to read everything right away, but I would suggest starting with the Overview, Editor, Graphics, Physics, and Scripting sections. These will give you enough info to get something happening. As you get more familiar with the basics and start working on a project or two, you can look through the other sections as necessary. Any time you have a question about anything to do with Unity I would suggest starting by searching the manual.

Unity also has the Learn With Unity section on their website, which has quite a wealth of information. In particular, have a look at the Tutorials. I would recommend starting here.

There are many different sources for tutorials elsewhere on the web, and many can be very good. The main thing to remember is that they may be using different versions of Unity. If you have familiarized yourself with the basics, you should be able to identify any changes you'll need to make to the tutorial's instructions, but this can sometimes be confusing. That's why I would recommend using the official Unity resources first.

As with most technical things, the best way to learn is by doing, so don't think you need to come up with an amazing idea for a game right away. Making something simple can still teach you a lot, and encountering and solving problems of your own can teach you more than simply following a tutorial.

If you encounter problems or get stuck and can't find the answer you need in the manual, then this site and the Unity Forums can be a good place to find more information. More often than not someone has already encountered the same problem and posted about it. A quick Google search with a description of your problem and the keyword "Unity" will more often than not lead you to the answer. Of course, if you're still stuck, don't hesitate to post here or on the forum. Just make sure you give the User Guide and FAQ a read.

Hope this helps!