This links are normally referred to as backlinks and the activity as link building.
Why Backlinks?
Link building helps in ranking your pages or websites rank higher in google search results.
Search Engine Optimization
Building backlinks is one of the major activities of SEO. SEO is a field where optimizers try to perform certain activities that would result in higher ranking of a target webpage in google SERPs.
Where to start?
Google is the answer my friend. Just google it and you'll find thousands of results (all are not useful). Read up the first 10 results you see and just get to it.
Need help?
You can also hire freelancers like myself to do link building or the whole of SEO for you. Platforms like Fiverr and Upwork are also there to find you best freelancers.
Good luck!
