If you mean how to use it ingame, then its quite simple.
Select 'Use Sanla' so it opens up on screen. The you need to type 3 things:
1. Grid Refence
2. Despersion
3. Number of shells.
So you would type into the Sanla something like this:
Ga35 100 20
The press the send button on the bottom right of the radio (forgotten which one exactly. Only that one clicks, so try them)
After a while you will get a reply confirming the message, and 20 shells will fall 100m around grid square Ga35.
Theres a reminder at the top of the radio. Its in Finnish, but you can read it from the numbers