If you create a survey with a repeat section upon publishing the software will create related features for you.
I'm new to this as well and it can be a steep learning curve but there are quite some good training resources, have you seen these:? https://survey123.arcgis.com/videos/
you may also search for 'advanced xlsform techniques' a 74minutes video which describes -amongst others- related tables.
success!
Bert -noob-