To get started, right click on the link and select ‘Save Link As…’ to download the software for installation (files from Arduino’s main page): (Windows Installer | Zipped file for Windows | Mac).
Current version: 1.8.5 [as of 13 Jan 2018]

Before using T-Scratch, Windows users will need to download and install the following:
1) CH340 USB driver; download (ZIP file) here.
2) DFPlayer drivers and library; download (ZIP) here 

(Note: The CH340 driver is hosted on Dropbox; left click the link and you will be directed to the download page.)

Step 1: Run the installer

Upon starting the installer, you will need to agree to continue with installation. Follow the prompts onscreen.

The installer will install both Arduino IDE and the USB driver required for ensuring that your program will be able to be downloaded to your T-Scratch module. Choose your preferred options for the shortcut.

Select a installation location, or use the default.

Arduino IDE and the USB driver will then be installed on your computer.

The system will prompt you again before installing the drivers. Click Install to confirm.

Once the installer is complete, you will be able to run Arduino IDE. Happy coding!