I am having diffculty understanding the move_base package

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I wish to use the move_base package to move my turtlebot3 robot autonomously to a desired co-ordinate point of a known map(I attained via SLAM gmapping). I have been going through the move_base documentation on ROS and still confused on how to approach(By the way I am new to ROS). I dont know if subcribing to the desired point to move_base_msgs/MoveBaseActionGoal is partcularly is the right direction to go, even then Im not sure how to get the robot to move to the goal after I have subscribed. Or am I going a wrong direction? I also have another issue where I want my robots initial position on the map to be the (0,0) cordinate on the global costmap. I hope I have explained my question well?