Simple Audio amplifier Using Transistors
If you want something simple to get started you could build this class A amplifier:  

 

(from this excellent site). 
\$R_E\$ stabilizes the DC setting, the bypass capacitor \$C_E\$ is needed to allow an AC signal to change the output, otherwise \$R_E\$ would try to keep the output constant.
A class A amplifier is not very efficient. There will always flow a current through it to keep the output at Vcc/2.