Host A (192.168.1.10) wants to send a packet to Host B (192.168.1.20) on the same LAN, but does not know B's MAC address. What is the very first step in the ARP resolution process?

ARP (Address Resolution Protocol) resolves an IP address to a MAC address within a local network by having the requesting host broadcast an ARP Request frame (to the broadcast MAC address FF:FF:FF:FF:FF:FF) containing the target IP address, essentially asking "who has this IP address?" The host that owns that IP address responds directly (unicast) with an ARP Reply containing its MAC address, which the requester then caches in its ARP table for future use — DNS (which resolves names to IPs, not IPs to MACs) and DHCP (which assigns IP configuration) play no role in this process.