Wind's tutorial on making a basic quest has some Osiris scripting in it:
http://larian.com/forums/ubbthreads.php?ubb=showflat&Number=615811#Post615811I use Osiris for almost everything if I can get away with it. It may not be proper if you are making a large scale game like D:OS 2 but it's just easier for small mods.
Some of the general stuff you can do with the story editor/Osiris:
Set up events based on walking into triggers (ambushes, waypoints, almost anything)
Script teleportation events
Set up conditions for quest success and set a flag when they are complete.
Databases aren't terribly complicated but I wouldn't worry about them at all for now outside of setting up dialogs.
The 3 basic parts are Events, Queries, and Calls.
Events: Purple colored, they allow you to script reactions based on things that happen.
Queries Red colored. These follow events, they go after the event in a statement. You can query multiple things in a statement using AND. Queries are used to get information and can see if the event should actually happen.
Calls (Green) - Calls do most of the things you see on screen. But sometimes offscreen too.
Simple example:
IF
CharacterLeveledUp(_Player) //This is the event
AND
CharacterGetLevel(_Player,3) // This is the query
THEN
ObjectSetFlag(_Player,"Level3"); //This is the call
DisplayText(_Player,"Level3");
So in this example, a character levels up. It checks to see what level that character is in the query. If the character has just leveled up(event), and the character is now level 3 (query), Then the character (call) sets the object flag "Level3", and displays the text "Level3".
The text must come from the translated string key. And you could use the object flag in dialog. Say your character is training, you can check that object flag to open up a new dialog node like "Oh I see you're getting stronger" or what have you.
As for your question of can you do things between object scripts and osiris scripts, yes you can. You can set flags in object scripts and set IF statements in Osiris to pick up on it.
For giving experience, that's also Osiris.
The #1 things I can say about using the story editor is press control + space. So in a blank space in a story file, type something you want to do something with. type character. Then press CONTROL + Space. This will pull up a list of everything you can do with a character.
Object is another common one. Type Object and press control + space.
Just an aside, all characters are objects. But not all objects are characters. So most(all?) calls that reference an object, you can use on a character. As I did in the example above.
With the lack of current documentation, the best way to learn how to use Osiris is to look at other scripts, such as those provided by the base game (need to unpack Shared.pak to get to these).
If you make a mod dependent on Origins you can see all the scripts as read only in the story editor without having to extract.