Hello! You can import an image as you normally would (either by going to File, Open or by dragging and dropping it into Pixelorama's window) and then changing the "Import as" option to "New reference image". Then, in the Reference Images tab (by default it is found next to the Canvas Preview tab, on the top right of the interface), you can modify the reference image by moving it around, scaling it, changing its opacity etc.
As for the crashes, are they related to the reference images? Do you have any steps that we can follow in order to replicate these crashes?
Sorry for the trouble caused. It crashes in version 0.11.3, but not the previous version you were using? If it's easy for you, we would appreciate if you could send us Pixelorama's log files (you can see how to find them here https://www.oramainteractive.com/Pixelorama-Docs/troubleshooting#pixelorama-cras...), in case the crashes output an error message.