Project are used to connect and authorize services and datbases in APIxFlow. Every connected service account uses one Project.
Flow is entity that represents one integration with specific business logic. For example you can build dedicated flow to read products records from MySQL table and another flow to push order into other table.

No, you can use free FlutterFlow tier to start building integrations with APIxFlow. But we recommend paid plan for development of production apps and websites to remove limitations of free tier.

Yes, APIxFlow contains free Starter and Trial options. You can test features with 14 days trial with 1 Project and 3 Integration Flows without requirement to subscribe and provide payment data. Also, you can subscribe for APIxFlow Starter - it's free with limit of 2000 requests per month. This allows you to try how integration works and become familiar with most product features.