I'm gonna get my phone later xD
Does it require to charge 8 hours first time?

The first 8 hour charge is important as the battery isn't "optimized" yet. The factory sends out pre-charged batteries because if left empty for long period of time, the battery tends to degrade. The idea is, the battery reaches it's full potential after a few charge/discharge cycles.

But doesn't the battery STOPS charging after it is full? Why must we carry on charging since it isn't really charging anymore?

This is an excuse and mistake that many people made when they are too excited to try out their "new toy".

And doesn't everybody that? Being EXCITED about the new buy!

The answer is that although your battery is "charged" and it doesn't charge anymore while sitting in the charger, but after about an hour or two, in the non-charging state, the battery will drain a little and can immediately activate a full charge again if it is sitting in your charger. This "fast charge, slow discharge" process happens a few times during your 8 hours.

If you simply start using your battery after the first full charge, the battery tends to remain in that "unoptimized" condition for the rest of it's lifespan.

If you use it after the 8 hours charge cycle, the battery is optimized and will stay in that condition for a long time before it starts its normal degrading.

Do a simple test with 2 batteries, one allowing it to sit for 8 hours, and the other being used immediately after it's first full charge. In a short period of time you should be able to see the difference in terms of how much a charge the batteries can hold.

Hope it helps!