Renaud,
You can read the on-line help for the Set Attribute VI by right-clicking over the VI and selecting "Help." The help will describe each of those parameters. In addition, you can search through counter examples for your 6713 by selecting from the menu bar Help>>Search Examples>>I/O Interfaces>>Counters. Any example that demonstrates the functionality of the DAQ-STC counter will work for your board. In addition, you will find examples on pulse train generation.
Hope this helps.
Regards,
Erin