Need to create a report where columns denote months, rows denote completed tasks across month.

Here is what you have to to:
1- Create a "task report" and make sure it uses a "process model" as context. and choose your process model.
2- Create the required columns (ie. User, Jan, Feb, ..., Dec, Total)
3- On the "Reports Option" window, check the "Group By" option next to the "User" column.
4- Click on the "Jan" column to edit its properties and do the following:
----- a. Put this in the definition field =if(month(task_completion_time())=1,1,0)
----- b. Choose "Number" as Formatting.
----- c. Choose "Sum" as Column Aggregation.
5- Do the same for each month but make sure change the condition to mach the month. For example for June you should use this as definition =if(month(task_completion_time())=6,1,0)
6- for the "Total" column, just put 1 in the Definetion field. And do the same as the points "b" and "c" from above.
7- Now switch to the "Filters" tab. And Check the "Completed" option.
8- That's it :)

Here is what you have to to:
1- Create a "task report" and make sure it uses a "process model" as context. and choose your process model.
2- Create the required columns (ie. User, Jan, Feb, ..., Dec, Total)
3- On the "Reports Option" window, check the "Group By" option next to the "User" column.
4- Click on the "Jan" column to edit its properties and do the following:
----- a. Put this in the definition field =if(month(task_completion_time())=1,1,0)
----- b. Choose "Number" as Formatting.
----- c. Choose "Sum" as Column Aggregation.
5- Do the same for each month but make sure change the condition to mach the month. For example for June you should use this as definition =if(month(task_completion_time())=6,1,0)
6- for the "Total" column, just put 1 in the Definetion field. And do the same as the points "b" and "c" from above.
7- Now switch to the "Filters" tab. And Check the "Completed" option.
8- That's it :)