I have read that linking back to other sites increase traffic and gets the other sites to link to you. So is linking back posting another site's link on your website? Just need confirmation cause I'm kinda confused lol.

Yeah. They're usually called affiliates or link exchanges. You just apply to become a site's affiliate, and if they accept, they put a link to your site on their site while you put a link to their site on your site. lol.

If you wanna put that on your portfolio then think again. A portfolio should stay classy, not be filled with advertising.

this is for my online magazine

Then it's appropiate. Mags always need some kind of ads.