What is the difference between the different versions of rails? How do I change my version of rails installed.

I will try to answer some of your questions.

You can install different versions of rails using the gem install rails -v 4.0.1 command, just as you wrote. When you do, from now on you can use that version for generating new applications that would use specific versions, the proper command is rails _4.0.1_ new odot (notice the underscores). You can try upgrading and downgrading Rails version in your project's gemfile and then running bundle update, but this might not be enough and some additional manual work could be required.

Rails is not a language - it's a framework that uses Ruby language. Ruby does not change that much from version to version, although differences are noticeable between major releases, like between 1.9 and 2.0. But Rails as a framework changes quite often and sometimes those differences are big (like the introduction of Strong Parameters by default in Rails 4, which makes it impossible to follow treebook videos with Rails above v3.2).

You have to learn to keep up with changes and adapt if you want to be a developer. You should learn both v3 and v4 (so go through ODOT and treebook apps), because in the future you might be asked to work with an older app that someone else wrote or even upgrade an app from older version of Rails to a newer one, so it would be good to know the differences and how things are done in those praticular versions. You will get used to it and it's not as crazy as you might think, Rails is quite established today, so changes don't tend to be that dramatic. You want crazy? I hear it's hard to keep up with Node.js and other hot, new JS frameworks, because they change a lot ;).

You can do both ODOT and treebook, just make sure you're using the proper version of Rails while generating the app or use pre-generated virtual machines from treehouse that have all the proper versions installed for each project.

Hey thanks for your reply I really appreciate it.Just some follow up questions.

when I install rails v4.0.1 (while I already have v4.1.4 installed) will that override the the version that I have installed? Or will it be like there are 2 seperate versions of rails installed (v4.0.1 and v4.1.4, where v4.1.4 would be the dominant one) and when I install v4.0.1 it's there but to use it I have to do 'rails_4.0.1_new odot'?

Going by that same logic just doing 'rails new odot' would mean I was using v4.1.4 of rails? Is that correct?

Also my ruby version is 2.0.0 while the treebook project says that it uses 1.9.3 for ruby will that be a problem for me? If so How do I get around it.

How do I learn to compensate for the differences bwtween the versions so that using ruby 2.0 and rails 4.0.1 I can make somethings similar to treebook? I guess what I'm trying to say is how do I bridge that gap in knowledge (and also learn about the changes that occur from using different versions of ruby and rails) so that what I learn in the tree book project will be applicable to all the other projects I do as a rails developer? I hope what I'm asking makes sense to you.

Thanks again for your help.

P.S I was wondering if you could explain to me a little bit about virtual machines.How did the experience of doing development on window lack for you?