Spore syringes contain spores (reproductive cells). They need to germinate first, then form mycelium, then colonise your substrate. This takes longer but is the most common starting point.
Liquid culture contains live mycelium already growing in a nutrient solution. Colonisation is faster because the mycelium is already active.
Both require strict sterility. If you're new to cultivation, spore syringes are the simpler starting point.