This tutorial is going to get you started with the Unity Editor. We'll look at the differences between Unity Free and Unity Pro, how to download and install the Unity Editor, create a Unity account, ending with getting Unity running. If you have any questions, please use the Disqus module at the bottom of this page.
The Unity Editor is available as a free download from the Unity website. It is your Unity Account (or lack of one) which determines if you are able to use the free or Pro versions. As you might guess, the Free version of Unity is free (I was shocked too! ;] ), and the Pro version has either a monthly subscription, currently $75/month, or a flat lifetime purchase at $1,500. This is just for a the standard Pro license, there are addons which you can purchase additionally, if you wish to take things further, but are not part of the necessary minimum you need to get Unity running. You can see all the pricing options on the Unity Store page.
Costs aside, there are differences to the features between free and pro. A common thought is that the free version is crippled or time limited in some way, to make you want to buy Pro. The truth is that the Unity Free is fully capable, and not locked in any way. You should try and think of Unity free as the standard edition, and the Pro version being the same but with extra bells and whistles. One caveat of the free license is that if you are earning over $100,000 USD per year, you need to be using the Pro license, but if your company is making money in this region, you should be able to afford Pro licenses anyway! Below is a list of some of the features you get with a Pro license, that you wouldn't get with the free license. You can see the full comparison of features between Free and Pro on Unity's License page.
Having the Pro license would basically allow you to make your game that little bit more polished, and provide a bit more control, but the core functionality of what makes Unity great is there in both license options. So, what do you need? Chances are if you are reading this, and just starting out on your journey with Unity and programming in general, the Free license option is more than suitable for you to get you started. If you have have prior game development experience from another engine/language and have the next "minecraft" ready to be made, you may want to consider a Pro license (and possibly skipping this section of the tutorial!), although there is nothing to stop you from creating the basic proof of concept of your game in Unity Free, before throwing down money on that license.
Personally, I have the Free license and until such time as I come across something I desperately need from a Pro license, or I somehow start making more than $100k/year, I'll be sticking with it! :)
Here we'll look at how to download the Unity Editor. Now, I only own a PC, so I can't give explicit details on how to do this with a Mac, but once you see how simple this is on PC, it shouldn't be too difficult to apply the same process.
While it's downloading, you can move on to creating a Unity Account.
In this section, we'll go over creating a new Unity Account. Now, as you'll notice when you first launch Unity, you don't actually need an account to use Unity. There is an option to launch Unity as a guest, and not provide any account details. So why would you need to create an account, if you're going to use the free version? Answer: The Unity Store. If you want to download anything from the Unity Store, you'll need to sign in with a Unity Account; free or pro. There are free assets on the Unity Store, such as the standard assets packs, which is useful to get you up and running with basic things in your early projects. You'll also need a Unity Account to make use of the Unity Community forums, too. If you're still not convinced you need an account, then please feel free to skip on to the next section. Below are the steps needed to create a new Unity Account.
Your account is now created, confirmed at ready to be used with the Unity Editor, Unity Store and the Unity Community.
So now you have downloaded the Unity Editor (see: How to get the Unity Editor), it's time to install it. As with the downloading, installing Unity is a pretty straight forward process. Follow these steps to install Unity:
Unity should now be installed. If you encounter any problems with the installation, please check Unity's Community for assistance. Alternatively, try asking in the Disqus module at the bottom of the this page as other users (or myself) may be able to help.