Selector without matchlabels

Hi I was referring the videos regarding services on the kodekloud platform and notice that while creating service manifest file we define selector under selector we define match Labels and then we define labels to create a link between pod and services but in the video match Labels was not defined under selector, author directly wrote the labels. Is it allowed defining service manifest file without match Labels, will it not create an error?

The selector in services works exactly as they show in the video: it wants a “map of string”. Just add sets of key pairs as shown, it will work fine.