Lock objects are use in SAP to avoid the inconsistancy at the time of data is being insert/change into database.

SAP Provide three type of Lock objects.  
- Read Lock(Shared Locked)
   protects read access to an object. The read lock allows other  transactions read access but not write access to  
   the locked area of  the table

- Write Lock(exclusive lock)
   protects write access to an object. The write lock allows other  transactions neither read nor write access to  
    the locked area of the  table.

- Enhanced write lock (exclusive lock without cumulating)
  works like a write lock except that the enhanced write lock also  protects from further accesses from the  
  same transaction.

You can create a lock on a object of SAP thorugh transaction SE11 and enter any meaningful name start with EZ Example EZTEST_LOCK.

Use: you can see in almost all transaction when you are open an object in Change mode SAP could not allow to any other user to open the same object in change mode.

Example: in HR when we are enter a personal number in master data maintainance screen SAP can't allow to any other user to use same personal number for changes.

Technicaly:
When you create a lock object System automatically creat two function module.
1. ENQUEUE_<Lockobject name>. to insert the object in a queue.
2. DEQUEUE_<Lockobject name>. To remove the object is being queued through above FM.

You have to use these function module in your program.