I am quite new to adword compaigns. I have seen some of the ads on Google having heading in 'bold'. Can you please suggest me how to do that !!
You can't do that. It's done automatically if those words match the search query. Just like the natural listing snippets get bolded on those search words.
To take it one step further if you have the same keyword in your body text that will also come up in bold. It pays to make a number of small adgroups with the common theme of placing the keyword in the title and in the body text of the ad for each ad group. This keeps the ads relevant and as the term that has been searched for stands out people are more inclined to click on your ad. There can be a lot of work involved in doing up your ads and adgroups but it really does pay off.
If you want to get really nifty you could try the Google AdWords API. With this you could then create an application which would automatically create the ad text based on your keywords - this would ensure you always had the bold.
When the search query is part of the ad-text, it appears bold. There is a very nifty trick called Keyword Insertion that can do what you want automatically. I suggest you ask AdWords customer service about it.