By default, a fresh Raspbian has the hostname or computer name “raspberrypi”. Maybe you want to change raspberry pi hostname. For example, if you operate several. Then you want them to differ in name.

Changing the hostname is not a problem in itself and usually done with a command. Unfortunately, most systems have a whole rat tail of changes. Unfortunately, you forget that or do not know it as a beginner yet. The changes are still necessary because otherwise it can eventually cause errors.