Quick answer: The A record connects your domain to your server's IPv4 address. Set @ and www to the same IP.
If you landed here: You have a VPS, webspace or game server and want yourdomain.com to point there.
Related
Webspace & domains: Order webspace · Register domain · nexorahost.com (Germany · Frankfurt · SSL included)
Frequently asked questions (FAQ)
What is an A record?
A DNS entry mapping a domain name to an IPv4 address. @ = root domain, www = www subdomain.
A record or CNAME for root domain?
For root (@) always use A record (or ALIAS/ANAME at provider). CNAME at @ is often not allowed.
How long until A record works?
With TTL 3600 usually 15–60 minutes. Globally up to 48 h → test with dnschecker.org.