There are two possible ways for you to advertise online. You can do paid for advertising or you can do it free of charge. I have tried paid for advertising several times and gotten a few results but it actually needs a large amount of research to get the best result. Regardless of what you're doing to make money online, you'll always be necessary to do research and that can always better your future earnings. Okay, back in line...
For paid advertising you are able to pay someone to advertise your existing ads or you can outlay cash to complete the entire project, meaning they'll create the ad and post it. Sometimes you receive good results and sometimes you get bad results, it truly depends on where you post your ad and just what category you want it in. Some ad sites are strict on their own posting so be cautious where you post. I would rather you learn to post ads for free and get top notch on what you're doing before hiring another person to complete the job.
However is posting with an ad website for the cost of nothing. Ad sites for example Craigslist, Backpage, eBay classified, US Free ad have free posting, but may are strict on in which you post your ad and what kind of content you fill in. For instance, sometimes you cannot post ads with titles like "Make Money when Today" to the job section. These websites just can't stand that, and they will violate your ad and ghost it, meaning it will have a hyperlink for you but will not be active, so pretty much your ad isn't showing. Some sites won't take a joint venture partner link or a link that forwards back to your site. There are videos and tools available to show you the way to advertise on these websites to make good money online, but with new restrictions coming, it get harder to publish nowadays.
Like earlier said, its best you learn to post freely and manually before you spend money someone else to get it done to ensure that if you hire the incorrect person to do this then you will know there mistake. If you're able to master the way of advertising you'll be able to really make a nice income online. You can even hire not just one, but an entire team to do it for you personally and generate a lot of monthly residual. This is called "outsourcing" which is totally legal for online marketing. But in the meanwhile, learn how to do free advertising and better your knowledge before you decide to advance toward make a nice income online.