How do resistor values affect the operation of a BJT transistor?

[ajack]

I'm really confused between saturation and amplifier. When will the transistor work in saturation mode and in amplifying mode? Resistors are the matters. We chose the resistors so that the transistor will work in saturation or amplifying. How can we chose?

 

[ranger]

We chose the resistors so that the transistor will work in saturation or amplifying. How can we chose?

Well you choose the resistor values depending on how you want the transistor to operate. As an example you may want to choose the q points so that the transistor is mid-point biased. These Q point values are determined by the (biasing) resistors used. The process of setting the proper operating(Q) point for a transistor/amplifier is called DC biasing. There are several biasing techniques, each with its own advantages and disadvantages. Here are a few links
http://www2.engr.tu.ac.th/~lvenus/classes/le210/biasing.pdf
http://www.allaboutcircuits.com/vol_3/chpt_4/8.html