In manual testing, you test the software by applying some manual efforts. Manual testing is mandatory and executed first on any new feature or software.
When that feature or software version becomes stable, we can automate it by writing some code scripts so that manual effort should not be done everytime when there is a bug fix or a new release. So basically, to reduce the manual effort of testing the same thing again and again, automation testing come to the rescue.
I hope it helps, if you need to know some more, You can ask me.