downloaded a jupyter notebook but it won't open
Have you installed it? ;-)
If you’re using a menu shortcut or Anaconda launcher to start it, try opening a terminal or command prompt and running the command jupyter notebook.
If it can’t find jupyter, you may need to configure your PATH environment variable. If you don’t know what that means, and don’t want to find out, just (re)install Anaconda with the default settings, and it should set up PATH correctly.
If Jupyter gives an error that it can’t find notebook, check with pip or conda that the notebook package is installed.
Try running jupyter-notebook (with a hyphen). This should normally be the same as jupyter notebook (with a space), but if there’s any difference, the version with the hyphen is the ‘real’ launcher, and the other one wraps that.
New to learning code: I started an online learning program for Machine Learning and Data Science. I completed the first project linear regression using a Jupyter Notebook  and Python 3 using Anaconda. It was saved as a ipynb file.
I downloaded and saved it on laptop(PC) but now it will not open. I think maybe I need to download something on my laptop that recognizes the notebook application.
Ok thank you to those who responded to my question. File opens from Jupyter Notebook just fine, I was trying to open from document folder. Thanks again!!