When creating a nether portal and going through it it creates a portal in the nether then vise versa , back to the over-world. although when creating a second portal, in either nether or over-world, it send you back to the first portal that was created (even if you are 8 blocks or further away). I had a portal link from the over-world  to the nether, then i went over 100 blocks north and created a new portal it spawned me in the same location in the nether, finally entering the portal in the nether will take me to the original location in the over-world (The first portal I built).