If you place a link on your site to someone elses site you give them a backlink. To build your own backlinks you need to get people to place your link on their site. A quick way to do this is to submit to web directories. Or if you are friendly with other webmasters you can ask them. You can also exchange links with other sites in your niche (you place their link in exchange for them placing your link).
As stated - backlinks are inbound links pointing to your site from another and directing visitors to your site. The more quality backlinks pointing toward your site that you have the more popular it will be considered.
back links are links coming from other site going to your site and a link from your site going to other site is a forward link
Im sorry, I usually try to help everyone I can but if you dont know what a backlink is, you are in the wrong forum