In more detail
GA4 is built around events. Every interaction (a page view, a scroll, a form submission, a purchase) is recorded as an event, and you mark the ones that matter to your business as key events, which Google previously called conversions. Google's GA4 developer documentation explains how data collection is set up.
For SEO, the most useful views show traffic and key events by channel, filtered to Organic Search, and by landing page. Together these show which pages attract visitors from search and whether those visitors take action.
GA4 and Google Search Console measure different things. Search Console reports what happens in Google's results: impressions, clicks and positions. GA4 reports what happens on your site after the click. The numbers won't match exactly, because they count differently, and because consent banners, ad blockers and privacy settings mean analytics tools don't see every visit. The two can be linked so that Search Console data appears inside GA4.
GA4's default data retention for detailed exploration reports is limited, so it's worth checking your retention settings early if you want to compare year on year.
Why it matters when hiring an agency
Analytics is how you'll judge whether SEO is paying off. Before an agency starts, make sure GA4 is installed correctly, key events are defined for real business outcomes, and you own the property. The agency should be added as a user, not as the owner.
Ask agencies how they'll report organic key events and revenue, and how they'll handle tracking gaps. If an agency can't explain the difference between Search Console clicks and GA4 sessions, that's a sign of limited experience. Our SEO ROI Calculator uses the same inputs (organic visits, conversion rate, close rate) that GA4 can supply.