You'll need to familiarize yourself with Tasks, Programs and Routines. In simple terms:
- A Routine is similar to LAD routines in the MicroLogix. However, instead of LAD2 that executes automatically, you must define a "main" routine. This will be the routine that executes automatically whenever that task executes. Other routines would be subroutines or a fault routine. Logic is always contained in Routines. Tasks and Programs do not contain logic themselves.
- A Program is a grouping of related routines within a Task. Sort of like a folder. A Task may have multiple Programs. Each Program has its own Main routine and subroutines. You can have up to 65,000 routines in each Program.
- A Periodic Task is essentially a container where you define how often it will execute its Programs and in what order the programs will run. The number of Programs depends a little on the firmware of the controller. I believe you can have 1000 Programs per Task. I think that used to be 32 when the Logix 5000 was first introduced. Some CompactLogix are limited to 16.
The number of Tasks will vary based on your controller. But I believe 32 is the maximum. Only one task may be defined as the continuous task.
Obviously, that is a very simple explanation. But that should get you started at least.