Hi Kjell, I've just signed up for the forums here but I've been using Soulseek on + off for about 20 years (high five to the dev team and communities for keeping this project going!)
Since no one has responded to you, I'll try to help. It's not a fun problem; just like the message says you've got to troubleshoot the networking ports and set everything up to forward properly, so that Soulseek can access what it needs to connect to others.
Where that phrase "port forwarding guides" is blue, that is a clickable link leading to a "Help" page with further clickable links for a lottttt of different brands of networking routers. If you can figure out which yours is and go click the corresponding link, it will help you troubleshoot this problem.
I can provide further advice on the software/computing side of this with regards to Linux or Mac installs, but I gave up a long time ago on trying to run a Soulseek application build on a Windows machine so I can't help there. I also don't trust Microsoft in terms of data privacy so I don't run my VPN-based activity on Windows machines.
Let me know if the port forwarding guides linked in your shared message correspond to your router, and if you are trying this on Linux or Mac, if so I'll try to help troubleshoot with you. Networking problems are a complicated PITA, but it's more of a local thing for our personal hardware setups and internet access points, less to do with "Soulseek" the graphical application that we install and open. You learn a lot of useful shit longterm though if you choose to tackle this and get it set up- I'm not a computer genius and I've worked it out with the port forwarding guides, so I think anybody probably can!