In Universal Analytics you may used to have events, goals and transactions (for e-commerce sites). In GA4 there are just events and conversions.
An event is a user interaction with your website or app. Events can include button clicks, video views, form submissions, downloads, add to carts. Events are tracked using event parameters, which provide additional context and detail about the user interaction.
Conversions, on the other hand, refer specifically to user actions that align with your business goals, such as making a purchase or filling out a contact form. In GA4, every conversion is an event, but not every event is a conversion. Usually, for e-commerce sites, a purchase event is usually marked as conversion by default. However, you can mark or unmark any other events as conversions too.
You should keep in mind that these changes will affect your metrics, such as conversion rate, and the changes are not retroactive. That means if you mark an event as a conversion today and unmark it a few days later, your data in default reports will be inconsistent. Yet you can still use filters and custom reports in Explorations to handle this.
You can mark and unmark events as conversions in the Admin > Events section.