Grouping tasks and resources
There are a few ways to approach grouping.
Select an item 
Add Child — Command-} 
Item becomes a group 
Add more items to the group 
Select some items 
Indent — Command-] (or Tab, depending on preference setting)
Items become children of previous item 
Select some items 
Drag them beneath an item — Note that the horizontal positioning determines the tasks' indentation level 
They become children of that item 