Every game is slightly different when it comes to joining a server, but genererally, the process is something like follows:
To connect to your server, login to the panel and click on your new server. From there, you can see the connection adress and - should you want to, manage the server by customizing settings. Paste the adress in to your game client (minecraft, terraria, valheim etc...) and connect. Upon purchase, your server details will also be emailed to the adress you've registered with on the panel.
If you need more specific details on how to access your server, don't hesitate to create a ticket and we will help you.