1. What we can do on giant gas planet? i notice that it can not be colonized and also nothing. Only the crystal and metal around them are good.
Any point of having giant gas planet?
Those mineral extractors you are talking about are called neutrals as they are in always neutral gravity well. They are very important as they are not effected by allegiance and cost no investment at all. They are significant boost to your economy especially early game . If you play vasari scouts with 60 AM can capture them and if you are TEC or Advent you need colony ship with 40 AM.
They are so important that in skilled games most of early battles are to secure them for your team. If you are vasari in skilled games it is not unheard of that you plant starbase in system with 3 of them just to keep control of them. Vasari early game are extremely dependant on them as they will decide if vasari that is battling advent will have to play defensively or be on offensive.
2. I found a short of "magnetic cloud" some in my star system. What we can do with it? any special or hidden artifact within it? does it disturb the trade chain?
It is same story as with gas giants. I might be wrong but I think that magnetic cloud disables all abilities so unless you are VR you cannot build star base inside it. If you are VR you can simply jump one in.
There is another type of neutral gravity well (ion something) that disables strike craft launch although skirantra ability scramble bombers works in it so those are only strike craft that work in above mentioned type.
Although I might have mixed them
3. I do explore on my planet and found a natural resources. How/Where can i check of what natural resources that i found? and what its for? How many kind of natural resource we have in SoasE ?
Either artefacts or natural resources can be find on planet info card. Difference is that artefacts work on empire scale while resources work on planetary scale. What artefacts do can be seen on research screen....
4. What is the different between natural resource and the artifact? What can we do with artifact? how many kind of them? because i notice that other empire has founded a powerful artifact on the notice screen.
Difference is that artefacts work on empire scale while resources work on planetary scale. What artefacts do can be seen on research screen.... Both of them give boost to your empire in one or other way.
They can be moded to handicap planets or empire as well as many SINS mods have done.