The primary difference between these two marketing strategies is granularity. Segments could be considered a broader umbrella, while several personas might exist within a segment.
Types of segments you can break your audience down by include: demographic, geographic, behavioral, and psychographic. You can use these to better manager your marketing channels to ensure you're reaching the most relevant new and returning customers.
Personas take a deeper look at specific customer archetypes who occupy these segments. These are helpful for crafting marketing language, content marketing strategy, and mapping your customer journey.