Once you login, click on your server name in the list, in this example the servers name is Your Server Name
Once you have clicked on your server you will be taken to the main Server Page which contains all of the server tools. You can start your server by clicking on Console > Start
If you are starting a Minecraft server you will be prompted to accept the EULA Agreement from Mojang
Once you click Accept you will be taken to this screen. Your server will be restarted during this process.