There are lots of ways to earn money online and advertising is one of them. There are some different ways to make money from online advertising and it depends on you as to how you choose to do it.
You could choose to earn money from a business that you already have by advertising online or start a business and advertise it online and if this is done properly it could earn you a lot more revenue. Advertising is expensive though and so it is important to make sure that you get the right balance so that you are still making a profit. Increase your sales by too small an amount and the cost of the advertising will be more than the extra profit made from the increase in sales and so it will not be worth it. However, if you get it right you could end up making a lot more profit by making a significant increase in sales. Some people would do this through a website and stop there. Others may advertise their website on other sites in order to raise awareness and they might also pay to be higher in search engines as well. These things can be expensive and it is important to monitor the costs and make sure that you think that they are worth it.
Some people make money in a different way. They set up a website or blog and then charge people to advertise on it. They might sell banner ads, text links or sidebar ads, for example. It is best to charge monthly, so that you can get a regular income from the advertising. In order to attract advertisers, you will need to have an informative website with lots of content which is added to and updated regularly. It will need to be set up and ad free for quite a while before people will be prepared to advertise on it.
Some people make money by helping others with their online advertising. They help them to try different search terms for search engine advertising so that they can get more traffic to their website which they hope will generate more sales. This can be a paid job or may be commission based depending on sale. Make sure that you are aware of which type of pay it before you take on a job so you are aware of the consequences and whether or not you will have a definite income or not.
So it all depends on exactly what you do as to how you make the money from advertising. There is not so much money in it as there was years ago, probably due to the increase in competition online these days. However, there are still people that can do well out of it and so there are possibilities for others as well. It is worth looking into it first to find out what is available and how much you might make out of it before you spend time and or money doing it.