Taking data from CT scan and printing 3D model

Operating system: windows
Slicer version: 5.6.1
Expected behavior: setting a ROI and creating a 3d printable model
Actual behavior: images are shown in 3 of the 4 windows, but have not been able to create a ROI image in the 3D window.

I am a newbie to 3D Slicer and DICOM files. I have scan files of my chest and want to print the ROI of my heart. I know how to 3D print once I have a STL. I am not able to create the model from my data.
Thank you for your support.

Have you been though the training material? Get things working with the sample data and then try the same on your data.