I'm a bit confused by the description of how to create encounters in the CRB. Say I want to create an encounter with 9 level 1 ghouls, what CR is it? And how would I change it to be a lower CR? Or a higher one?
And just by looking at an encounter, what is a good way to determine CR? For example, what would be the CR of dungeon room with 4 shadows?
For multiple creatures that are the same CR, you increment the overall CR of the encounter instead of tallying up individual XP totals. Two CR 5 creatures is a CR 7 encounter, for example. Both your two examples would be about a CR 7 encounter. It's all in one of the first charts here. Adding the advanced template to monsters gives each creature +1 CR and is very quick and easy to do. Putting monsters in terrain or under conditions that works against them somehow can lower CR (the reverse also applies for increasing monster CR when terrain and such impacts the party). I'm not sure if there is a good way to gauge the difficulty of an encounter just by looking at it if you want to go beyond simple CR. It probably all comes down to experience, party make-up, house-rules, and a whole host of other factors.