Create a secondary data connection to your list...while creating data connection select get data from SharePoint list, then select all your required columns whichever you want to display in the form. Once data connection creation is done, go to the secondary data connection, and drag and drop the items nodes to form.
We can filter the list items data by applying the filter on the secondary data connection.
See my other answer here on how to filter the SharePoint list items and display them in the form.
How to save the data in SharePoint list?
If you are customizing the SharePoint list using InfoPath form... we don't need to create a secondary data connection to submit the form data back to SharePoint list, the inbuilt main data connection will take care... however, if you want to submit the data to a different list, you need to create another secondary data connection with Submit data (while creating the data connection you will get this option), then on the submit button rule as action select this data connection to submit the data.
How to create a secondary data connection to submit the data in the SharePoint list?
- Click on the Manage Data Connection from the right side Fields panel.
- Click on the “Add” button in the “Data Connections” wizard. In the next screen, you will get the below:
Create a new connection to:
Submit data – This is used to submit the InfoPath form data to the
Receive data – This is used to read the data from a SharePoint list (by default, this will be selected).
Select the "Submit data" radio button
In the next screen, you will see “Select the source of your data”,
select as SharePoint library or list.
Enter your SharePoint site URL in the “Enter the location of the
SharePoint site” box.
From the available lists or libraries, select your list.
Click on the Next button and continue...
For details refer to the below article:
How to auto populate field in InfoPath based on another field