Hi all
I have some atmega8 that installed arduino bootloader, but that is all. And i want use it to make an arduino circuit board, I found but haven't found any document/tutorial guiding the way to do.
So what are needed to build ? And then how to connect them ?
Apologize for simple questions because i just come with arduino a few days and havent had any experience of arduino 
Start with an Arduino Uno.
By trying to make the ATmega8 work, you get yourself into a lot of troubles. That will take the fun away of using Arduino.
When you have an ATmega8 with an Arduino bootloader, do you know for which frequency the bootloader is ? 8MHz or 16MHz ? Is the bootloader for internal or external clock ? Is the bootloader a 'NG' type with reset button to upload a sketch, or is a new Optiboot with DTR-reset to upload a sketch ? Is it really a ATmega8 ? or a ATmega8P or ATmega8PA ? or other type ? then you have to make a new board in the Arduino settings and perhaps change the configuration file for the uploader.
Should I go on ?
Okay, well then, if you are an advanced electronics guru, then search for 'barebone' Arduino.
Start here : https://www.arduino.cc/en/Main/Standalone.
But don't connect AREF to something.
Here's the basic connections needed. Leave off the FTDI & ICSP connectors if you want, and the crystal & caps if you're using the internal oscillator.
So pretty much 3 0.1uF (100nF) caps, 10K reset pullup resistor, and 5V/Gnd connection. Not much!
This PCB/Design should work with an ATmega8:
There are plenty of tutorials/etc describing "minimal" arduino designs, and any of the ATmega328 designs should work equally well with an Atmega8 used in place of the 328.