As JD mentioned, first thing you need to do is resolve your hub and devices not showing up when you log into the IDE. Once you can actually see your hub, devices, device types, etc you will have to find the custom app in the depth of the internet realm 
Fortunately, you could search or post this forum for a specific need. I gather you want to add Nest to ST. Search this forum for Nest and one of the links you will find is:
Word of caution. This thread has over 500 posts. If you are confident enough to proceed without reading each and every post, you could quickly jump to https://github.com/tonesto7/nest-manager/blob/master/README.md for installation instruction for the Nest Manager.