To build your user set:
1. Use an Add New Data Element comp to set up a counter variable (int) initially set to 0.
2. Set up a looping structure to verify that the counter is less than the count of the listbuilder output (count should be in the stream)
3. In the loop, use a Get Item By Index comp 3 times (using the counter var as input) to get the appropriate row of first name, last name, and email
4. Advance the counter by 1. Thus you get the 2nd row, 3rd row.... nth row.
As far as "saving" user data, why not use a User Defined Data Type (integration library)? Make a User data type with last name, first name, and email properties.