Control flow is where you define operations and order of execution of those operations. for example you put two operations: execute t-sql command on a database and send mail. then you define order of them with Precedence Constraint for example the t-sql statement should be executed and then if it succeeded mail will be send.
Data flow is where you define data stream; where data comes from (data sources), how data should be transformed (transformations) and where data should be loaded (data destinations). you can pass data from a component to another components with Data Paths.