Digital marketing is the use of digital channels — search engines, social media, email, websites, and paid advertising — to connect businesses with customers. Unlike traditional marketing, it’s measurable, targetable, and adjustable in real time. Core channels: SEO (free organic traffic, highest long-term ROI), paid advertising (immediate results), content marketing (builds trust and compounding traffic), email marketing ($36 ROI per $1 spent), and social media (brand awareness and community). Start with one or two channels and learn them well before adding more.