When you start the Emu68 Imager you will be presented with the options screen:

The Run Tool button will remain red until you select the required options.
Options that are mandatory are the SD Drive to write to, The OS version you intend to install, your desired screen mode for the RTG driver, and the paths to both the system ADF images and your Kickstart ROM image.
Bear in mind that if you are installing AmigaOS 3.2.2.1 or 3.2.3, you will need both the base 3.2 ADFs as well as the hotfix/update ADFs in the same folder.
If you want to quickly create an image for your Pistormed amiga then you can leave most things on their default setting and do the following:
Refresh Available Media button.Click to set Kickstart Path button. Click the Check button to validate you have the correct files.Click to set ADF Path button. Click the Check button to validate you have the correct files.Run Tool button remains red then you have not set the required options. Pressing this button when red will inform you of which options you have missed.Run Tool button should turn green if there was enough space on the disk you launched from. If you have insufficient space, the button will turn yellow and give you the opportunity to select a different drive. Bear in mind that you will need enough space available for the entire image - which can get quite large for bigger SD cards.Run Tool button and follow the popup windows to start the tool. A console window will open showing you the current progress.