For now, only the totals of all the rolls in the chat area will be shown, though this will change in the future. If you want to track rolled results, you can right click on any of the words in the chat box, select "Add Name," and assign it to "Checks & Tags" for any user.
As of version 1.1.0, Roll20 has gained support for the freeform style of table creation. This means that you can now create tables on Roll20 by simply clicking and dragging points (the middle part of squares, or circles) onto a piece of white paper. When you are done, you can click on the red "Save As Current Layout" button in the upper left to make your table the current layout. To switch back to the old tables (mystery dice!), click on the red "Save As Previous Layout" button in the upper right.
Certain things can prevent dice rolls from working. There are dice engine system options that can prevent dice from being rolled (listed below). These options can be changed in the Options drop-down menu in the upper right corner of the web page, under Misc. d2c66b5586