Why add capacitors and resistors to an NPN transistor circuit

[jasum]

http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/npnce.html#c3

Here is the explanation of npn junction in hyperphysics
1,what important to add the cap. inside the input and output circuit?
2,what difference after I select the remove the bypass cap. in the website?
3,what is the purpose for adding the R1 and R2 in the circuit?

Thank you a lot!

 

[SGT]

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