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Always when we want to represent the magnetic field of the earth we see a similar image:

enter image description here

My question is, what exactly does this show? What are the blue and orange lines, what do they represent? Why are they curved like that? I have a vague idea about field lines, but I do not fully comprehend this. An explanation would be appreciated

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The origin of blue & orange lines (in your Wiki image) represent North & South poles of Earth. Indeed, Earth could be imagined to be a magnetized spherical shell. Those are the magnetic field lines (a concept introduced by Faraday). Field lines are introduced as an aid of visualizing electric & magnetic fields. They're commonly referred to as "lines of force". They have several characteristics associated with them - like beginning at north pole & ending at south pole; don't intersect, etc.

You could draw infinite number of magnetic field lines within a given region of space. In magnetism, these curved lines simply imply that a compass placed in any of these lines would deflect tangentially to the curves indicating magnetic poles of Earth. These lines could be drawn using a bar magnet itself..!

Sadly, I must also add that your question is possibly related to Magnetic field lines already asked here...

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