My advice is to not start this if you have limited funds and don't understand how it works very well. This is very much a for profit business for the owners of the search engines and as such they will have a lot of ways to trip you up if you're not savvy to the way it works. So make sure you know what you're doing before you get started. I tried it once when I was a newbie and ended up owing a lot of money I couldn't afford to invest and lost my virtual shirt in the deal.
One of the best ways to get your advertising out is to blog and write articles, or use other people's articles with their permission, which can be very easily obtained by asking. Most people are very flattered if you want to use their articles as long as you give credit where it's due. You can link their keywords to articles you find online and have a lot of rich backlinks. This is way better in my book than Pay Per Click.
You might also consider Pay Per Click email marketing, safelist marketing, and traffic exchange or ad exchange marketing which can also be very low cost and often free.
If you still wish to use pay per click sites like Google Adsense, make sure you have a big enough budget to pay for the highest cost keywords, because there is a very stiff competition for these words and there are some big companies that are able to pay in the thousands for the best ones so you may not be in their league. Most often the little people like us have very little chance of stepping into this form or marketing unless we have a unique set of words that aren't being used much. But like I mentioned earlier, you can always Google the words pay per click and shop around and find sites that maybe don't charge as much if anything. So just try the waters and see how it goes.
Feel free to comment back if there's anything you need or don't understand.
My advice is to not start this if you have limited funds and don't understand how it works very well. This is very much a for profit business for the owners of the search engines and as such they will have a lot of ways to trip you up if you're not savvy to the way it works. So make sure you know what you're doing before you get started. I tried it once when I was a newbie and ended up owing a lot of money I couldn't afford to invest and lost my virtual shirt in the deal.