The question you are asking is very broad. I cannot give you specifics because your question is not specific. So here’s quick walk through for getting up and running.
1.) Install you favorite version of Linux
2.) Download Zaptel & Asterisk from www.asterisk.org
3.) unzip and compile Zaptel & Asterisk
4.) you can accomplish step 3 by executing the following commands at a terminal.
tar zxf zaptel-1.0.9.tar.gz
tar zxf asterisk-1.0.9.tar.gz
5.) You can now configure Asterisk by editing the files in the /etc/asterisk folder. You can also configure the Zaptel driver by the /etc/zaptel.conf file.
6.) As root type ‘asterisk -vvvvgc’. That will start asterisk running.
There’s a brief method of getting up and going with Asterisk.