am new to kdenlive !
i tried to edit few video clips...
added few sec video in track 1 and muted its audio
added few sec audio of mp3 file in track 2
and rendered output file in avi format !
unfortunately my 55sec video was of size 220MB
6min video was around 1.5GB size !

how to configure to get a better quality with small file output size ?
please help me out...

please instruct me in steps to configure !
am new to kdenlive !

AVI does not mean, you get a small file size. The file size and quality depends on the bitrate.

higher bitrate => better quality => larger file size
lower bitrate => lower quality => smaller file size

This formula is the most common one. If you leave the bitrate constant and render to a smaller picture size, the quality of the picture gets better (less information to be packed to the same amout of data => better quality). Or use a codec with higher compression, then you can leave the picture size and lower the bitrate to get the same quality.

You can calculate the size of your final movie by this formula:

(bitrate [bit per second] / 8) * movie length [seconds] = filesize in bytes.

Example: A movie with 60 seconds rendered with 2000k results in a file of 15,000,000 bytes (~15MB).
Your rendered file must have a bitrate around 40,000,000 bit (40,000kbit) which (I bet) is more than the bitrate of your camera.

In this forum you wil find some threads dealing with quality and file size. Be brave and search!

how do i configure ?
i mean , how do i change that bitrate and stuff ?
please... help ?

You can configure the bitrate and stuff in the render profiles. How to change and create your custom profile, please search this forum, it has been explained before.