Snapshots are, hence the name, snapshots of the development of a major update to Minecraft: Java Edition at a given time. Today's snapshot is called 20w13a – the first snapshot released in the 13th week of 2020 – and contains a few new features.
A long established fact in Minecraft is that compasses only work in the Overworld dimension, which is the dimension you spawn in when you first start the game. However, there is now a way to have direct navigation in other dimensions: a new block called lodestone has been added, crafted using chiselled stone bricks and a netherite ingot (netherite is a new ore added in earlier snapshots), and using a compass on lodestone will cause the compass to always point towards that specific lodestone, which will be very useful when exploring these dimensions.
The other new feature in this update is the strider. Striders inhabit the expansive lava lakes that make up much of the Nether. In fact, striders can walk on the lava! Striders can be saddled to create a very useful mode of travel over the lava lakes, although the new warped fungus on a stick must be used if you want to control the strider's movement.
In a sense, striders are basically Nether "boats", and that's exactly what they were made to be, says developer kingbdogz:
Lava boats were the obvious [addition], and Striders ... are much more exciting!
These features, as well as many more, will be available in the full release of version 1.16: the Nether Update, which features a complete overhaul of the once-barren Nether with new biomes, mobs and blocks, and is coming soon to all editions of Minecraft. You can test out the new features by enabling snapshots in the Minecraft launcher.