At its simplest the, more links to a website the higher a site will appear in the results. There is more to the topic but as a starting point this is the best way to view the subject.
Discovering links to your own business is not especially difficult - it is one of the options available from Google analytics.
Knowing where your competitors get links from is a greater challenge, but one which Website-Doctor.com can help you with.
The links which Google approves of most are the ones created by people who have bought / interacted with your service and have been delighted and have wanted to share that good news with others.
Maybe they are restoring a car and you have taken their old steering mechanism and made it like new. They are delighted and want to share that fact.
Links which have been bought whilst this might work in boosting your visibility in Google, go counter to the spirit of what Google is trying to do, which is measure genuine popularity of a site, by the number of links to it.
Links are akin to the fuel in a rocket. They power your website up the results in Google.
First step know who is linking to you.
This is not static. Websites come and go as do pages, along with their links.
If your competitor's websites have been around a while chances are they will have links and those links will have been picked up.
Website-Doctor can supply you with an Excel spreadsheet with a list of their backlinks.