Social media marketing is connecting and engaging with other social media website users in order to do marketing of your business, products, services etc... That connection via postings and conversations is used to build your trust and trust of your brand or product, which should result in more traffic to your sales pages and actual sales of your product or services.
It's known that marketing is in use for many many years before internet existed, but with mass engaging on social media sites, you having opportunity to do internet marketing worldwide from your office. you can do it even free if you built large audience (friends / followers) or you can outsource it to freelancers and social media influencers to boost your sales. Yeah, that's all about business. But to build quality and large audience, friends lists and followers, you can't always only slap them with your ads, you have to be friendly, helping and engaging in what they have to share with you and others.
Best social media sites are already know by most of you, Facebook, Twitter, LinkedIn, Pinterest, Google plus, Instagram and many others. On most of these sites, it's almost same rules in making friends and building your trust.
Connection between SEO / SERP and social media websites exist via social signals and here is how it work.
If you struggling to build large enough number of friends or followers, you can always choose some of Seoclerks services to help you out.
If you have more specific questions regarding social media marketing, you can ask, below here and me or other Seoclerk members will guide you in professional manner.