ports are closed

[dogukan kuru]

So i found this program 3 days ago. For downloading it works great. I found a lot of stuff that i wanted. I have also seen people taking from me too which is great. However i tested this software with 6 people including myself. On 3 it works perfectly fine, we can exchange files with each other no problem. On other 3 tho. It does not really work.

currently when  i test my ports it says

IP: 159.146.66.6 Port: 49899/tcp CLOSED. Your router and/or Soulseek client needs to be configured correctly.

You may want to check this list of port forwarding guides for instructions specific to your router model.

Don't forget that you need to restart your client if you modify your listening port.

apparently i gotta do something with ports. However i do not understand any of that.Can someone help me ?