The welcome screen is the first thing you see when you open the client (the .exe file named "Sanctuary 1-4d" etc). At the top of the display, your client will show the current version it is running on. Be sure to check the Main Page to ensure that this is the correct version.
Refer toFig. B1 and notice the text at the bottom reading "Press any key to continue..." This is what you will see between battles and after any in-game notifications (such as a level up or mob encounter). As implied, any keystroke on the keyboard will allow you to continue, however, the [Enter] key seems to be the most common.