The squad leader PDA or in short - SQL PDA is a virtual items - means you don't need to actually give it to the player, that any player who have more than one other unit under his command gets.
The SQL PDA is accessible from the action menu or by defining a key bind in MCC (by default right Ctrl + Page Down).
After opening the SQL PDA the player can double click any location next to him to open the PDA interface.
The basic use of the PDA is to spot enemy whereabouts By double clicking on the assumed location of the enemy and selecting the type of enemy and the size, squad leaders can share info about known enemies with ease.
The markers will be visible to all players from the same side as the squad leader.
Enemies' markers will automatically deleted after 5 minutes.
Squad leaders can choose to use the Call Support option to mark the area needed support as support can be a request for pickup or a request for ammunition or even requesting a fire support on known enemy location. All active player from the same side as the squad leader who placed the markers will see the support markers and may respond accordingly.
In construction option squad leader can request to build battlefield emplacements such as: HMG, mortars or even FOB.
For more details about construction check here.