Download Image
Open the Docker interface of your Synology Device, search for linuxserver/speedtest-tracker in the Registry and download it.
Create Directory
Create a local directory (i.e. /volume1/docker/speedtest-tracker) which later can be mapped to the docker container.
Start Image
Launch the image once the download is completed.
Map Ports
Map the ports to available ports.
Map Directory
Map the directory you created earlier to the mount path /config.
Finish
Review your settings and click "done".
You can now access Speedtest-Tracker via http://YOUR_IP_ADDRESS:8080 or https://YOUR_IP_ADDRESS:8443.