The six levels get quoted everywhere and explained almost nowhere. Here is what each one means in terms of what you can actually do, rather than in the language of assessment criteria.
A1 and A2: surviving
At A1 you can introduce yourself, ask simple questions and understand slow, clear speech aimed at you. You cannot follow a conversation between two other people. At A2 you can handle routine situations — shopping, directions, ordering, simple exchanges about your background. This is enough to travel comfortably and not enough to make a friend.
B1 and B2: the useful middle
B1 is the first level where the language becomes genuinely useful: you can deal with most situations that come up, describe experiences, and hold a conversation as long as nobody rushes. B2 is where you can work and socialise in the language. You follow native speakers talking to each other, argue a point, and read most things with a dictionary nearby rather than in hand. Most learners who say they are fluent mean B2.
C1 and C2: comfort and precision
C1 means you rarely search for words, understand implicit meaning and can use the language flexibly for professional purposes. Getting here from B2 takes as long as everything before it. C2 is not native-level. It means precision and ease across almost all situations, including subtle and unfamiliar ones. Plenty of native speakers would not pass a C2 exam in their own language.
The levels are not evenly spaced
A1 to A2 might take a few months. B2 to C1 can take years, because each level covers roughly twice the ground of the one before. This is why progress feels fast at the start and glacial later, and why comparing your months to someone else’s level tells you almost nothing.
Use the levels to describe where you are, not to measure how fast you should be moving. What matters is whether you can do the things you wanted the language for.