There are two types of shells in World of Warships Blitz, these are high-explosive (HE) and armour-piecing (AP). The ballistic models for these two types of shell are the same. You will find that the the shell's in-game tracer may not coincide with the actual trajectory, this has been done intentionally by the game designers in order to better visualise the shooting process.
High-Explosive (HE)
The most common shell type is high explosive, commonly referred to simply as HE. These shells have a strong steel case and an instant fuse that bursts immediately upon hitting a target. High explosive shell are particularly effective at knocking out modules, especially AA mounts, and start fires which can over time cause a considerable amount of damage.
Armour-Piercing (AP)
This type of shell will only do damage if it penetrates the armour of the ship. Once the AP shell has penetrated the armour the fuse of the shell is initiated. Historically the fuse times are calculated in a way that would allow the shell to explode after traveling about ten or so meters after passing through the armour so that it explodes in the middle of the ship.