how to advertise online?

[Kesavan]

What you're talking about is Google Adwords.

You first have to create a google adwords account, enter in your bank account details and choose the keywords you want your website to appear for.

But I would highly discourage this.
Why?
Let me explain with an example-
Your product maybe a hotel at Paris
Mr.A wants to visit Paris and need a place to stay so they type in "Hotels at Paris" in the Google search bar and your website appears on the right column.
Mr A clicks on your website and you are charge 1$ (more or less depending on the competition) for that click.
Now this is okay. Mr A and 19 other people looking for hotels in Paris click on your website daily. So you're charges 20$ a day. That's fair. But what Google does is, besides these 20 people, they add 80 more FAKE clicks to collect 80 $ from you. Their reporting system is manipulated.

You'll be spending 100$ a day instead of 20.

Besides just because you pay for having your website advertised on Google Adwords doesn't mean it'll always appear. It depends on other factors, like keywords on your website, your page rank, your bidding amount etc:- that you're gonna have to take care of.

Bottom line is, it's much more result-oriented to have SEO work done through natural link building to appear on the first result page of Google instead of Google Adwords.
Searchers can tell apart from advertisements and actual relevance to what they are looking for.
Instead of expensive advertisement go for the cheaper, more effective one- SEO
the best one I could find is http://www.seoart.in
Their packages start from 100$ a month.