connect()

The connect() function is redux is a way to connect React component to the Redux store. It allows the component to read data from the store and dispatch actions to the store to update the state.
It does not modify the component class passed to it; instead, it returns a new, connected component class that wraps the component you passed in.

connect accepts four different parameters, all optional. By convention, they are called:

1. mapStateToProps?: Function
2. mapDispatchToProps?: Function | Object
3. mergeProps?: Function
4. options?: Object

• Import connect:
  First, you need to import the connect function from react-redux.

• mapStateToProps: This function specifies which parts of the state the component needs. It takes the Redux state as an argument and returns an object with the needed state data.
  

• mapDispatchToProps: This function specifies which actions the component can dispatch, It takes the dispatch function as an argument and returns an object with functions that dispatch the necessary actions.
  

NOTE :Your component will receive dispatch by default, i.e., when you do not supply a second parameter to connect():

• mergeProps:
  mergeProps?: (stateProps, dispatchProps, ownProps) => Object
  This function should be specified with maximum of three parameters. They are the result of mapStateToProps(), mapDispatchToProps(), and the wrapper component's props, respectively:
• stateProps
• dispatchProps
• ownProps
  

ownProps: are just the messages directly sent from the parent to the child, without going through the Redux store.

mapStateToProps: mapStateToProps?: (state, ownProps?) => Object​
If your mapStateToProps function is declared as taking two parameters, it will be called whenever the store state changes. It will be given the store state as the first parameter, and the wrapper component's props as the second parameter.

mapDispatchToProps:
mapDispatchToProps?: Object | (dispatch, ownProps?) => Object
If your mapDispatchToProps function is declared as taking two parameters, it will be called with dispatch as the first parameter and the props passed to the wrapper component as the second parameter, and will be re-invoked whenever the connected component receives new props.

• options: options?: Object
  In Redux, the options parameter isn't a built-in part of the connect function. Instead, it might refer to various options or settings that you can configure when creating your Redux store using createStore.
  
  Here are some common options you might encounter when configuring a Redux store:
• middleware
• reducer

• Connect the component: You wrap your component with connect passing in mapStateToProps and mapDispatchToProps. This returns a new component that is connected to the redux store.

To know more about connect() function