Hi, I have got few questions about common textures:

1. What's different in Caulk and Caulk Shadow?

2.I've read a lot of tutorials about portals adding to map, but ... What are portals doing? My map compiled very nice without these ... ?

I don't know for sure but the difference between the two Caulk textures is probably that one casts a shadow and the other does not.

As for portals. They don't have much to do with how your map compiles, they help it run smoother. Portals help tell the player's computer that certain sections of the map don't need to be drawn when they cannot be seen, essentially.

Soo ...

What about outdoors? Let's imagine: road with minefield on both sides, after that few trees, bushes etc. portals will be only on the road, right?
I thought, that portals are only in rooms, not outdoors, maybe im wrong?

If you have the CodUO tools version and open up mp_foy that comes with it, you will notice they portaled a lot of the outside to break up the map. For Cod2 it probably is not as necessary seeing as you can not drive vehicles, that i no of, so maps are just not as large.