What each record type does
A and AAAA records point a name at an IPv4 or IPv6 address. CNAME makes one name an alias of another. MX lists the servers that receive email, lowest number first. TXT holds text such as SPF rules and site verification codes. NS names the servers that hold the zone, and SOA has its serial number and timers. CAA says which certificate authorities may issue certificates for the domain, and SRV points services like SIP or IMAP at a host and port.
SPF, DMARC and DKIM in plain English
SPF is a TXT record listing the servers allowed to send email for your domain. It may use at most 10 DNS lookups, counting every include, so this check follows each include and adds them up. DKIM signs each message with a key published under a selector, such as google._domainkey.example.com; your email provider tells you the selector. DMARC, at _dmarc.example.com, tells receivers what to do when a message fails both, and where to send reports. Start with p=none, read the reports, then move to quarantine and reject.
Why records can look different elsewhere
DNS answers are cached for the TTL shown next to each record, in seconds. After you change a record, resolvers may keep the old answer until that time runs out, so different tools and networks can disagree for a while. Switching the resolver above lets you compare two large public caches.