Profoundnet is the Profound Bond tumblr, found here where member posts and creations are reblogged and PB fests/projects are promoted. The blog only follows those who are members of the Profound Bond discord server, and thus become part of the tumblr network. Once you are part of the network, you can use #profoundnet in the first five tags on any of your destiel/gen SPN creation posts, and the post will be reblogged by the Profoundnet tumblr.
If you are not part of the network, or your post is not Destiel/Gen, you are still able to use the tag to get more potential views, but it will not be reblogged to the Profoundnet tumblr/