Downloading BYOND is easy to do!
When you get to the download page it's recommended to grab the BETA version of BYOND which includes everything you need to get started.
The reason for this being that the BETA version gets updated more often and usually includes more features and fixes than the stable version. It is also typically required if you are looking to contribute to an existing project in BYOND.
You can grab either the Windows or Linux version of BYOND; however, this guide assumes you are using a Windows OS.
For an easy installation simply click on the Windows button under BETA. This will download an executible file that you can run after the download is complete. The defaults are just fine unless you want to change the location that BYOND is installed to.
Once that's is all finished, you are ready to get started with the DM language!
An installation to make your life much easier when coding in DM would be VSCode. It's an open-source multi-platform code editor that includes a lot of features and QOL improvements that make it substantially better than the editor that comes with your BYOND download.
You can get VSCode from here. For this download, we suggest using the stable build as the insider edition updates frequently and can mess with your projects if you aren't experienced enough. As for the actual installation process, it's the same deal with BYOND. You can change the options if you like but if you are unsure of what you are doing the defaults will work just fine.
Once you finish installing and open up the editior be sure to login with your Microsoft account so you can access the Extensions Marketplace. There are a few goodies there that you will want to grab in order to work with the DM language and BYOND itself.
The absolute bare minimum that you'll need is the BYOND Extension Pack. You can either click the link to install the pack remotely or you can click on the icon that looks like 4 squares with one popping off on the left of your screen. This pack includes the tools needed to properly write and run DM code. It also includes some assistive tools to help you out when you write such as auto-completion and syntax highlighting.
If you want to grab even more tools to assist you there is always the Goonstation Extension Pack. Contrary to the name, you don't have to only use this pack for Goonstation. It includes some extra tools that aren't 100% needed but just provides a bit more assistance and some extra functionality that will be very useful to you later on if you decide to join the BYOND or SS13 community.