Hi,
i build my tomb level in Wed! But when i start the compiler, a error-message comes! What must i do, why i have so much portals? What are Portals?

Thanks

Portals are the measured blocks by the engine for rendering the scene.
Too many means your block level is too large so you will need to split it up and make several different levels out of the one level.

In other words, your level is too complex.

but i only build a temple, whats wrong?

To many blocks not corectly aligned probably or jutting out from the edges etc.
Try to align them perfectly.
If you have lots of little blocks for detail, convert them to 'detai blocks' so they wont be rendered as veiwable portals.
Then in your compile options, reduce the tabs dealing with 'tessalation' towards the FPS range to reduce portal count, keep experimenting with these untill you get a balance for FPS and nice looking shade, not shadow.

If you have complex corners and intersections, you will also get a high portal count (refer to the manual regarding portals) but most of it can be scaled back with carefull level design.

can we see how many "portals" we've used somehow?

sounds like a pretty bad artificial limitation.

you can if you manage to successfully compile (try with a smaller and simple tonb) by pressing F11 twice. They show up as red lines, in-game view, on both static and dynamic blocks (wmp and wmb geometry).

This is not a limitation, it is common and is dependant on your level building skills.
A good level design and the skill to use the software determins your outcome.