Welcome back to Esri Community! To get started, you'll want to navigate to the places where you're interested in starting a discussion or posting a question. You can use the top navigation menu where it says All Communities and browse the available communities for products, developers, and more.
For ModelBuilder and ArcGIS Server, for example, you'll select All Communities > Products > All Product Communities, and you can browse the available product spaces.
From there, you'll see boards by content type. Go to the question board for that place and click Create A Post to post your question to the question board. You can also search for places to jump to other areas in the community.
For more information, check out How to ask a question and How to write a good question that will generate responses.
You can find more assistance in our Community Help Documents about how to use features around the community.