a question with pc

for example,i connect some sensors to arduino,and arduino also connect to pc, but now,how can arduino know which infomation form pc control it's own sensor?

Sorry. I just cannot understand parts of this.

Sensors connected to Arduino

Arduino connected to PC.

Okay so far.

It is the "control" parts. Tell us more about what you want to happen. Don't worry too much about HOW it will happen... just tell us, specifically, WHAT is being sensed? What should happen? When?

sorry about my english. :) "Sensors connected to Arduino" means:One arduino connect Many Sensors to control them.

"Arduino connected to PC." means: i want to use computer to control arduino with usb, computer send a message to arduino,then arduino can control sensor.

arduino only send "HIGH" OR "LOW" or other numbers to sensors, but it don't know the message from computer can only control which sensor.

thk u!

If English is a problem try typing the question in your own language in www.google.com/translate and provide both languages like this.

(output of Google translate)
Si l’anglais est un problème, essayez de taper la question dans votre propre langue dans www.google.com / traduire et de fournir les deux langues comme celui-ci.

PC sees Arduino through serial port so you have to write a program for PC which sends serial commands and a sketch on arduino which reads these commands and does what you need.