CLARIFICATION

All Apple products are designed in california and assembled in china ... What does it mean exactley ?

It means precisely what it says. Apple products are conceptualized, designed, tested and marketed under the brand name Apple. China lacks the technical know-how to design smart electronic gadgets but since the labor cost is dirt cheap, Apple outsources the assembly of the components to make the final product to a Taiwanese company Foxconn that has operations in China.

Remember that China lacks the technical know-how to even manufacture the components that are put into Apple products. These components come from different sources in Japan, Korea, Europe and the USA. All these suppliers send their components to the Foxconn facility in China so that the final Apple product can be assembled.

For example here's the typical manufacturing of iPhone:

 

iPhone Primary Contractors  - a partial list

Software and design	Apple	USA
Assembly	Foxconn?, Quanta, Unknown	Taiwan
TFT-LCD Screen	Sanyo Epson, Sharp, TMD	Japan
Video processor chip	Samsung	Korea
Touch screen overlay	Balda	Germany
Bluetooth chip	Cambridge Silicon Radio	UK
Chip manufacture	TSMC, UMC	Taiwan
Baseband IC	Infineon Technology	Germany
WIFI Chip	Marvell	USA
Touch screen control chip	Broadcom	USA
CMOS chip	Micron	USA
NOR Flash ICs	Intel, SST	USA
Display Driver chip	National Semi, Novatek	US, TW
Case, Mechanical parts	Catcher, Foxconn Tech	Taiwan
Camera lens	Largan Precision	Taiwan
Camera module	Altus-Tech, Primax, Lite On	Taiwan
Battery Charger	Delta Electronics	Taiwan
Timing Crystal	TXC	Taiwan
Passive components	Cyntec	Taiwan
Connector and cables	Cheng Uei, Entery	Taiwan

As you can see, China has no role other than providing cheap labor who would assemble the components coming from myriad sources.