Depending on the kind of marketing you’re buying, you could pay per click (PPC), pay per view (PPV), pay per acquisition/action (PPA), or just pay a flat rate for each instance, for example with an influencer you generally purchase a certain number of posts.
With some old-fashioned display advertising, you might just pay to keep your ad displayed for a certain amount of time.
Twitter is interesting because if you’re good at it, you should be able to generate tons of organic (read: free) interactions, but at the same time, people can be very wary of brands co-opting what they see as part of Twitter’s culture. Offensive or ill-timed tweets can also blow up in a careless social media manager’s face. “Good at” twitter means more than just able to make conversions or generate retweets, it means an understanding of and sensitivity to the medium.
You can create static or dynamic campaigns, small or big campaigns, retargeting campaigns, campaigns with a huge spend or campaigns with a tiny spend. There are Facebook lead ads, which makes it super easy for people to give you their information. Link ads, that send people to your website. Or ads that contain in-Facebook product catalogs that do automatic retargeting. It’s a lot to learn, but it’s also easy to get started.
AdWords are an old-school paid traffic source that still offers huge potential rewards, though the cost per click is often high. The basic concept is that you choose keywords that you think your potential customers will search, and you bid on putting your ad as one of the sponsored search results at the top of the page. Of course, AdWords has gotten way more sophisticated as the online advertising world has evolved.
There are a lot of options, and figuring out what works for you can take some tinkering. A mix of organic and paid traffic, such as Babylon Traffic, is usually the most effective way to grow a business.