Hi Neha,
Here are a few things that might get your started... and keywords you can google for....
Code:
var cb:ComboBox = new ComboBox();
var dp:DataProvider = new DataProvider();
cb.dataProvider = dp;
dp.addItem({label: "Option 1", data: 1});
dp.addItem({label: "Option 2", data: 2});
dp.addItem({label: "Option 3", data: 3});
addChild(cb);
And some attributes you might need for your combo box (cb.**)...
.width, .rowCount, .prompt, .dropdownWidth
You should also be able to style it using a TextFormat();
Hope that helps!