The startup configuration file is loaded into memory as the running configuration file when the router boots up.
When you enter the privilege exec mode and then the configuration mode to issue configuration commands, you are working on the running configuration file. There is no need to load the startup configuration file again, unless you have special reasons to do so.
After completing the configuration, you should save the running configuration file into the startup configuration file using the command "copy running-config startup-config".
KPLAB