Why is Unity not functioning properly?

So I’ve decided that I want to start using Unity as I felt that it was a more legitimate game development tool than some of the ones I’ve used in the past. I went online, looked up some tutorials on how to get started and I thought everything would go along swimmingly. I guess Unity seems to have some gripes with my computer however, as the damn thing doesn’t want to work properly.
I’ve been using Lynda.com for my Tutorials on using Unity 2D, I’m only on the fricken’ Essential Training video and it’s already failing on me. I’m copying the script down line by line, everything looks perfect. For some reason, some commands such as Vector2 and such don’t seem to function the same way they do in the tutorials I’ve been watching (I’d show comparison screenshots, but I deleted my script when trying to get it to work/ out of frustration.)
I keep getting error messages when I hit play to test out if it works.
I’d really like to know what the issue is. Could it be Unity, my computer, Monodevelop, etc.?
(Is it important to mention that every time I try opening a script in Monodevelop, it always tried opening in Visual Studio?)
Please help with this. If there’s really just no fix, I’d like to know some sort of respected/legitimate substitute 2D Game Development tool that I can use for commercial use.
Thank you in advance.

I also get an error message whenever Monodevelop opens up.

Well the visual studio thing I’ve had happen too, when you install Unity one of the check boxes on that big list of things you want is visual studio, and if you get that it makes visual studio your default code editor.

As for the script erroring without seeing the actual code, it could be in Java and the tutorial in C# (or vice versa). It could also be just a simple syntax issue, maybe from a unity update because the tutorial is a bit old. If you hit play and you get errors, even after deleting the script, that might be because the objects that were using that script or other scripts were still trying to reference it, and now it doesn’t exist. That’s my best guess, hope it helps