Here I've done the centre square-in-a-square block. Plus I've attached the middle strips together.
Here I've attached additional pieces for those middle strips and am working at the next centre square-in-a-square.
Here the centre square-in-a-square is complete and the triangles have been added to the middle strip set.
Now you attached the next border. There are set in seams, don't be scared. I put together a more detailed tutorial on it.
Then I add the final triangles and we have our next block finished.