The simple answer is that yes, you probably should watch the first movie before sitting down to see the second one, especially since the films are packaged as a trilogy.
The film does a great job explaining the returning characters’ relationships and history together, but there are certain details that will be lost on you if you skip the first movie.
The biggest cause for confusion for someone who hasn’t seen “Into the Spider-Verse” is likely the main villain, The Spot, since that’s where his origin story is introduced.