As mentioned in the title, I'm currently unable to bring up any pictures from the initial "posts" menu. I can however open them up in another tab and they work just fine.

If it's any help, I just created my account a few days ago and I'm unable to post my art or join the Discord as of yet. Don't know if that has anything to do with it though.

Also, while I have your attention, is there anywhere that I can go to learn how to better utilize this site? An "e621 For Dummies", if you will? Definitely different from the other user-friendly places I've been.

Have you accidentally changed your mode?

If you're on mobile, scroll to to the bottom of the page and change the dropdown box beneath the "Mode" heading to "View".

On desktop you can find this directly beneath the search box

you can't post images on e6 or join it's discord server because your account is too new, IIRC you need to have been here for at least a week before you can do either. as for an "e6 for dummies", there is nothing that would teach you about how this site works on a general level, however the wiki homepage links you to several pages with useful information, and you can search through it to find information on tags and certain other stuff.