For most collections in the DAP, you do not need to sign in to access them. If something comes up in a search result, you can read about it.
If you see a padlock icon, this means that the files are either restricted or embargoed:
If you want to request access to the files, go to the collection's description and look for the "Contact" section:
Need help with the Data Access Portal? Please contact Research Data Service Support at firstname.lastname@example.org or phone: +61 2 4960 6086