I’ve been using the free Wolfram cloud for a while; it is actually very capable for small projects. Several tips:
It can’t upload any files, put the data somewhere online, then use Import[url] to get the data
Each command can only run in a limited time (several minutes?), and sometimes reducing the size of data can help the job run through, for example, ImageResize[image,Scaled[1/2]].
Learn some keyboard shortcuts, especially on cell formatting: Keyboard Shortcut Listing for the Wolfram Cloud.
The most important thing: download your notebooks and also save a pdf copy. The file expires after 60 days, the user can’t open and download the expired files.
You probably can guess what happened to my files, they are all expired. I am not complaining here, it is free service anyway. To avoid this issue, I decided to try Free Wolfram Engine with Jupyter Notebook. They can be connected by WolframLanguageForJupyter. I am not going through the installation part; it is well documented for each product. I’ve created a sample notebook ImageStitch.ipynb with JupyterLab (a better interface than the classic Jupyter notebook). (Note: if it doesn’t load properly, try to reload it again). I may try other connectors later, the one used here is directly from Wolfram, however it doesn’t support auto-completion.