%target = findClientByName(%target); // finds each client name and sets it as %target
This actually takes the input, cycles through all the clients in the server and then returns the closest match to the input you gave it.
%player = %target.player; // if the player is targeted
No if statement here. This is just making a new local variable, taking the client you just found, and then assigning the client's player object to the local variable.
if(isObject(%player)) // if the player is an object
This is making sure that the client's player object exists. A client is like a person's soul; their connection in the server. A player is just the body that the soul is put into. The player can die. But if the client dies then that person is no longer connected to the server. Here we're making sure that the soul's body is still alive.