[GTALUG] help moving a hard drive into a different computer?

Hi folks, Sorry rather behind. request is simple, as my short term computer solution is starting to fail. while a new one is being built for me, I have no idea of that timeline. between the landline issue and my cell phone having someone accessing its sim code to dial it remotely, my computers are my contact with the outside world. Task will be simple for a knowledgeable person. Any ideas? Freecycle cafe used to be terrific for such small tasks, no idea of a good door now however. Thanks, Karen