How to configure the port for garry's mod server

Hello. I would like to ask you for help. I would like to create for garry’s mod server but only that I would have a problem. How do I open the doors. How do I configure the server from the router? I have a Fritz Box 3272. Thank you in advance!

You can Google on how to do it for your specific router brand.

https://www.google.fr/url?sa=t&source=web&rct=j&url=https://en.avm.de/service/fritzbox/fritzbox-3272/knowledge-base/publication/show/3244_Setting-up-the-FRITZ-Box-as-an-IP-client/&ved=0ahUKEwiynJmX44bSAhXD1xoKHVP5C0MQFggeMAI&usg=AFQjCNHYrnuPBf6-ndtkPlg_RPYONoL_Jg&sig2=OAYvw_3f5146lT1KcvmkLQ