If you feel you messed up, or just can't get it to work from where you are now, the best thing to do would be to start over with a brand new (Noobs or Raspbian) disk image from
formatting link
Just wipe your card clean and write the new image. After you log on and have gone through the raspi-config options, immediately (and later regularly, say bi-weekly) do "sudo apt-get update && sudo apt-get upgrade".