You probably just installed the whole Flutter by following the getting started guide neatly, and see your build of the test app getting stuck at "Initializing graddle...".
Do note that the first launch of graddle will take some time, even on a good computer and fast internet (for me it was around 20 minutes).
Before you stop and try to rebuild, I suggest you enable verbose building output. (Scroll down) so you see what is actually happening.
Also make sure you have set your system PATH correctly.
So I was for once in a long time again busy with web development, trying out the new PHP 7 in combination with xampp. Being frustrated by the slow page servings on my decent hardware equipped localhost, I went out to find the bottleneck.