What is a pairing?
A pairing or 'block' is a collection of flight legs and/or activities that are put into a kind of assignment block. The pairings have a crew composition.
The main purpose of creating pairings is to speed up the crew assignment process. If the crew planner knows that the same crew will operate multiple flight legs, it makes sense to collect these legs together in a pairing and assign all of them at the same time.
Note: Once the roster has been published, you have the option to keep or split the pairings. The process of how to split pairings is described further below in this document.
Creating a pairing
Pairings are built using the flight legs and designated crew complement.
To create a pairing, open the roster Gantt and load the Leg Gantt in the upper window and the Pairing Gantt in the lower window.
Highlight the flight legs in the schedule and drop them in the lower window to create a pairing.
Note: The pairing is created on a row showing the default pairing name when using the default pairing consolidation mode. If using a different consolidation mode, it will rename the rows based on the parameter used for consolidation. To change the consolidation mode, go to User Preferences / DefaultPairingConsolidate.
To save your pairing(s), click the Save icon 
.
Roll out a pairing
To roll out the pairing, highlight the whole pairing in the Pairing Gantt, right-click click, and select copy.
In the copy dialogue window select rollout and the date, weekly frequency, and end date. The start date will be on the day the pairing was created.
If you deselect the check box "CopyOnlyInFuture", you can define a start date in the past. If you uncheck the option "OnlyExactMatch", flights that differ with their start and end times in the given amount will be considered for the rollout. If left checked, the rollout will be done on the days when the flights match by the minute with the reference date.
Click the RUN button, N-OC will now roll out the highlighted pairing.
Add reference activities to pairings
In this case a deadhead activity has been added after a flight that ended on an outstation.,
To add such a reference activity, select the pairing, choose the reference activity from the dropdown menu,
activate the Assign Block-Activities icon 
and drag the mouse on the Gantt where you want the activity.
You can now edit the reference activity by right-clicking on it in the pairing.
Splitting a pairing
In some cases, you want to split a pairing. Right-click a pairing and select 
In the pairing Gantt, you will see a red line under the pairing indicating the pairing is split and doesn't exist.
On crew, you see the individual sectors.
Before split:
After split:
Multi-split
From the roster wizard select Split roster block.
Mark the pairings you want to split and click the SPLIT button.