Can someone explain Portals and Sectors? I read the documentation but still have no clue, they sound useful but I don't know what they are?

They're for level efficiency. Basically, when you're in one sector, the props in particular other sectors won't be rendered. Obviously it's a bit more complicated than that, but yeah.

Say you have two rooms connected by a door. Each room can be a sector and the door becomes the portal. When the door/portal is closed, the game will understand that it's impossible for you to see into the other room so it no longer has to do any rendering calculations for that room. When the door/portal is open/active, you may be able to see from one room to the next (from one sector into another sector), so SWBF2 has to spend the processing time rendering the graphics for both rooms instead of just one.

If don't use sections and portals, SWBF2 doesn't know you can't see into the other room when the door is closed, so it always takes the time to render both rooms.

So for example if i have a very very big map it could cause performance problems so if i add such things we can make the map to work more smoothly.
Thats very good idea.It will be good to get some tutorial

Ginev wrote:It will be good to get some tutorial

Those come shipped with the ModTools and can be found in the documentation folder;)
(Or here...)