A blogger: "I want to divide footer into 3/4 columns as like in your 'goodcomputersoftware.blogspot.com'
The above demo blog uses template from Ourblogtemplates.com. If you just want to modify your existing template, Amanda of BloggerBuster has a very good instructions at How to add 3 columns to your footer which should work for any template as the new columns uses fluid width.
I tested her instructions by modifying my 4 column Minima template into 4 column Minima template with 3 column footer and you can see the result at Star Self Improvements. The 3 columns at the footer had been used to contain widgets from Amazon and may take some time to load.