No problem - that is just one of the first steps in the learning curve of ED. We've all been there.
You have to control the menus through the keyboard, and <space> is the default for selecting the current menu item.
As for the relog/buy game issue, there's a couple of threads for that. There's also this support article
The "Please purchase/redeem Elite Dangerous to continue" message will appear when the launcher does not detect Elite Dangerous game access. If you have purchased Elite Dangerous for S...
customersupport.frontier.co.uk
which seems to indicate that, if it only happens occasionally, there's a connection problem somewhere in the triangle between your PC, Steam's server and whichever server Frontier is using for your account verification.