The short list.
IF YOU LEARN ONLY TEN, LEARN THESE
PUBLIC_HTML
Anything here is publicly downloadable. Never put backups or records in it.
NAMESERVERS
Where your domain's DNS records are managed. Changing these changes everything.
A RECORD AND MX RECORD
Where your website points, and where your email points. They are separate.
IMAP VERSUS POP
IMAP keeps mail on the server across devices. POP downloads to one and removes it, which is why mail appears to disappear.
SPF, DKIM AND DMARC
The three DNS records determining whether your mail reaches inboxes.
INODES
The file count limit, separate from disk space. Email and cache exhaust it while space looks fine.
ENTRY PROCESSES
Simultaneous requests. Reached first on small sites with slow pages.
WEBHOOK
How a payment gateway tells your shop a payment succeeded. The most common cause of orders not updating.
AUTOSSL
Must be run after adding any domain or subdomain, or the certificate will not cover it.
BACKDOOR
Why cleaning a compromised site fails when only the visible damage is removed.
WHAT TO DO WITH ANY TERM YOU DO NOT KNOW
Ask. A support conversation goes faster when both parties mean the same thing.
