The Newick string will be written in the text area located above the canvas.
All the nodes of a valid unrooted tree must have the degree greater than or equal to 3.
A valid rooted tree must have one internal node of degree 2. All other nodes of a valid rooted tree must have the degree greater than or equal to 3.
You can then visualize the phylogenetic tree corresponding to the provided Newick string using the Newick viewer program available on the T-REX web server.
More details on the Newick format