Here is a quick tip on the importance and how to use a stitch marker when crocheting continuous rounds.
Stitch marker (crochet) - Wikipedia
Amigurumi tips and tutorials, hookabee
How to Crochet in the Round (Magic Circle & Chain Ring) - Maisie and Ruth
Using a Stitch Marker in Amigurumi [video tutorial] – PlanetJune by June Gilbank: Blog
How to use a stitch marker for Amigurumi - mycrochetchums
Amigurumi: Basic Techniques - Dandy Bee Makes
Almost Perfect Color Change in Spiral Rounds
How To Use Stitch Marker In Continuous Round Crochet
How to Use Scrap Yarn as a Stitch Marker • Salty Pearl Crochet
How To Use Stitch Markers in Amigurumi – PlanetJune by June Gilbank: Blog
Working in Continuous Rounds (Spirals) - Learn to Crochet - US Terminology - Video 10