I have to guess at what "in front and behind there base" means.
But resistors are need to bias the transistor into it's linear region, if it is intended for use as an amplifier. There are several ways of doing this, and the reference lists them. The best one is the voltage divider, which applies a (relatively) fixed voltage to the base. this causes a relatively fixed emitter voltage, as that is the base voltage minus about 0.6 volts. Then a fixed emitter resistor yields a fixed collector current. And with the proper collector resistor, puts the transistor into it's linear region.
If you don't understand the above, review ohms law and how transistors operate.
Look at the link at the bottom of my post. Do you mean R? and R?? If that is the case then the answer is that each BJT design will have the need of a unique bias voltage to set the operating point of the BJT amplifier. (You need to cause the B-E junction to be forward biased and the emitter may need to be at some design voltage, as well.) Two such circuits may need two different bias voltages. Three such circuits may need three different bias voltages. It doesn't take long before you find you need dozens of bias voltage supplies and that gets crazy-minded very quickly. Another part of this is that even if it were easy and cheap to provide these specialized bias voltages, you'd still need to isolate them from the base with a resistor, so that the preceding circuit driving the amplifier doesn't drive a very low impedance supply.
The wonderful thing about a pair of resistors forming a resistor divider is that they can produce any arbitrary bias voltage AND provide an impedance that won't swamp out the input signal for the cost of just two resistors. It's like getting two things in one and for almost no cost. It almost doesn't get any better than that. About the only way to improve on it with only a few cheap discrete parts is to bootstrap it. (Another discussion.)
If you are talking instead about R? and Rc, too, then the entire topology is in question (there are many possible arrangements now) and the need depends upon the application.
Maybe this will make it easier or be to basic but this is my take on it.
There are two things happening with a transistor. One the DC operating voltage. The second being the signal.
Well all the resistors which transistors endure has the reason to stabilize the operating voltage.
Most signals are AC signals, ie they are a varying voltage centered at zero. Transistors are electric valves that do not amplify at zero current. They require resistors to create an offset called bias to move the transistor input/output current into the middle of their operating range, where the input is added and the result is a output current and/or voltage that is a stronger copy of the input.
It is the biasing for transistor so that we can control its operation point. To understand more about it, read basic transistor textbook.
Because usally they are needed to be set to the linear region which is above the cut off region and bellow the satuation region
Your question is too vague. You need to provide more information to get a good answer.
Using the example of a standard transistor (with one collector, base and emitter), why is it that you typically need resistors both before (in terms of coming into contact with positive voltage first) and after the base (with the one after just connecting closer to the more negative end)?
Don't know if this varies by situation or if there are universal reasons for this but I'm observing a circuit diagram and trying to interpret the reasoning behind this.
