I'm not sure what Lynda.com is, but normally just going to college and medical school in the US will mean you pick up everything you will need to be prepared for residency. If you're a non-traditional student and grew up without learning to use a computer, then you likely haven't picked those things up unless your job or personal life required them, though you would likely still need to use them in medical school.
You definitely don't need to "master" PowerPoint or Word, but knowing the basics is essential--you will need to be able to develop at least simple PowerPoint presentations. You should know how to write a CV in MS Word, how to write a manuscript if needed, etc.
You will need to know how to navigate the internet quickly, look up research/review articles.
If you're a one-finger typist I'd say the first thing you should do is take a typing class--right now. There's really no way you will be able to survive in residency if you're hunting and pecking with just one finger. Unless your program still uses paper charts, but many programs that still have paper charts still have some form of EMR (electronic medical record), and I'd anticipate most hospitals with paper charts will be moving to an EMR soon. Most jobs will also involve working at a hospital with some form of EMR, so unless you definitely plan to become a psychiatrist who starts their own practice and write everything by hand, you will need to know how to type.
I'm probably missing a number of things, but the most essential is really learning how to type fast, and then learning how to use the EMR of the program you match into--those are things you need to know and will be using on a daily (really an hourly, or minute) basis and have a huge impact on your efficiency.