Starting to use Teamviewer

I am a newbie to Teamviewer and I have tried to find a solution in the forum so, if I'm repeating posts that have been answered, I'm sorry, I just haven't found them.

I have been able to install Teamviewer 13.1 and it works much quicker than competitors but I'm now trying to help a friend to set the progamme up on their computer and all we get on the bottom of the window isunable to connect to the internet. I know the computer is connected because we can browse the internet through Firefox and Edge (She's running Win10). Is there somewhere in Teamviewer that I should be looking for a setting to tweek? Or, is there another problem I haven't spotted?

Thanks for your help in anticipation.

Ben