There are over 100 API endpoints that you can read and write data to. These include endpoints for configuration, inventory and production including entities and transactions.
For example some of the sales and inventory endpoints are:
SalesOrderDespatches
SalesOrderDespatchItems
SalesOrderItems
SalesOrders
StockGroups
StockItemAliases
StockItemAllocations
StockItemLocations
StockItemPrices
StockItems
StockItemUnitsOfMeasure
You can access a comprehensive list if you login to the app and go to: https://app.vinsight.net/Metadata.json?$top=999
Also each endpoint documents the properties, their attributes (type, nullable, length etc) and the key values it has by appending $metadata to the query string eg: https://app.vinsight.net/SalesOrders?$metadata