Liquid spawn is mycelium expanded into an optimized nutrient solution and grown out, most commonly used in tandem with sterilized grain bags. Liquid culture is a great way to jump into your mycological journey as it is easy to use and doesn't require a traditional lab space. Just inject your culture into sterilized grain bags or jars and watch the mycelium grow.
Find Liquid Culture here: https://www.fieldforest.net/category/liquid-spawn-culture-bank