Blueprints are two things:
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A way to configure a “prefab” configuration of game objects, put together to make a “full actor.” For example, you can bundle up a particle system, a light, a sound effect, a mesh, and a projectile movement component, to build “a grenade” as a blueprint. You can then subclass that “grenade” in child blueprints to change mesh, trajectory, amount of damage, loudness of sound, etc.
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A way to “wire up” said composed objects, without having to dive into C++. When you build a grenade out of components, you need a little bit of logic – “three seconds after throwing, hide the mesh, play the particle system, sound effect, and light flash, then clean up/delete the grenade object.” That level of logic is super easy to do in Blueprint. Similarly, you can do “when I walk close to a door, animate it to be open, then when I leave the door, animate it to close again” using a detector volume, a timeline, and a door mesh, plus a small amount of blueprint wiring.
It is very, very, helpful to understand what blueprints can do, and where they are strong. It allows you to easily get “things moving” on the screen in interesting ways, without having to bootstrap a bunch of C++ class knowledge or worrying about object ownership. It essentially shows you “what the goal is” of future C++ development.
It turns out that, because wiring is a Turing complete programming language, you can write an entire game in Blueprints. I wouldn’t recommend it, but it is possible – any tool can be pushed harder than it should be, if you really want to. (See also: using Javascript to build single-page apps.)
Once you understand more of what the pieces of the engine are, you can learn C++, and how to build the components that you will end up using in your actor blueprints. At that point, you need to learn not just C++, the language, but also the macro/code generation package that Unreal puts on top of C++, and THEN you need to also learn the C++ class library that makes up the engine. This is a lot of work, and really hard if you don’t know how it all is supposed to fit together – don’t start there!