To connect your gateway to The Things Stack Community Edition, it has to be configured to properly forward the traffic to it, and it also has to be added/registered on The Things Stack Community Edition. Instructions for adding gateways are available at The Things Stack - Gateways.
To add a gateway, you will need to provide Gateway EUI and its Frequency Plan. Some other optional parameters can be defined. Learn how to add gateways using Console or CLI.
If you are experiencing issues while adding gateways to The Things Stack Community Edition, see Troubleshooting.