Can't use Sourcetree

[Dan Katz]

I have installed Sourcetree on my Windows 10 desktop.  A collaborator has created a bitbucket remote repository.  I can sign on, access the bitbucket repository, download his entries.  However, I have not been able to clone this remote repository to a local directory.  I can hit the Clone button on my bitbucket window, but when I try to clone for https, it just looks at me.

When I try to use the Sourcetree app, it comes up, with a promising looking window, but disappears in a couple of seconds.

I've tried all kinds of stuff, e.g., entering the git clone command bitbucket shows me on my console, but it does not recognise 'git' as a command, nor does it recognise 'clone' if I don't use 'git'.

Does anyone have any ideas what I'm doing wrong?  I'm happy to provide more info if needed.