Hello!
There have been a lot of questions recently that have also been answered recently, and it seems that people are having trouble finding those answers. So I put together this unofficial FAQ for those exact questions with as thorough answers as possible, including quotes. Hope this helps! 
If you have or know of a question that should be on this post that I somehow missed, please send me a message or respond to this post.
These FAQs are listed in no particular order.
1: My project won’t stop loading. What do I do?
Your project is constantly “loading” because it doesn’t have an HTTP server set up to host your code, website, bot, etc. on. One way to create an HTTP server is to use Express in your server.js file (or index.js; the main JavaScript file of your Node.js project). @etamponi has an excellent example below on how to set it up.
2: I deleted my project. How can I get it back?
Whenever you delete a project it’s not gone forever. It’s actually really simple to un-delete. One way is to wait for the “ Deleted” notification that pops up in your project editor, in which you can then click Undo 💣. This feature is not an original Glitch feature, meaning that it did not exist when Glitch was first released. @pketh released this feature on December of 2017 (link below).
The other way of undeleting a project is to simply scroll down to the Deleted Projects 
section of your profile. There you can find a list of every single project that you’ve deleted, and buttons to undelete them.
3: Can you change my Glitch username?
4: Is PhP supported?
Sadly not yet; the Glitch team is hoping to find people who are fluent in that area so that they can get it up and running to use in projects. However, there are two projects that enable you to use PhP, but without them it’s not possible.
There are also other experimental projects that introduce other languages such as Ruby and Java. And according to @anon1813117 (I don’t know myself haha), “you can use any language that is installed in your container, you do not need a pre-built project.”
5: What is that padlock thing?
The only “padlock” I can think of is the lock in the project editor:
If that’s the one you’re seeing, that’s where you change your project to Public and Private. When Public anyone can view the code just like you with https://glitch.me/edit/#!/hello-world, except where hello world is your project’s title. Since everyone can see the code, they can edit it then, right? No, thank God. The developers at Glitch pulled a smart and didn’t allow anyone except you and those you allowed to edit your project. Today, if you try to edit a project you’ll remix it instead. If your project is Private then no one can view your code…through the editor, anyways. You can still view a project’s code with the “View Source” option (only for websites to my knowledge).
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Again, I hope this helps! If anyone finds something wrong such as a typo or simply wrong information, more information for a topic, or another topic to add go ahead and respond to this topic or send me a message and I’ll get it added!