There are many ways to lose life points. Every player starts out with 2000 at the beginning of the duel. Some cards say to inflict this much damage to your or your opponent's life points often after a certain requirement has been fulfilled or to pay as a cost for a certain effect. The most common example of losing life points though, would be if one player attacked another player with a monster with atk points higher than the opponent's atk position monster. The difference between their atk points would be inflicted to the person with the lower atk point monster.
I know only Magic Cylinder
No. But if there is, it is probably already banned.
8000. But in the anime the usually have either 2000 or 4000
There is no legitimate Yu-Gi-Oh card with 'infinite' for the ATK, however there ara a few fake cards with it.
Yes, but only if they have no monsters left on the field- or If you have a spell/trap/special monster that allows you to attack them directly.
I know only Magic Cylinder
8,000 Life Points.
Well at the actual show each player starts with 4000 life points. But in real yu gi oh card games like you get yu gi oh playable cards you start with 8000
Yes, you can use these back-to-back in Yu-Gi-Oh.
There is no upward maximum.
Yes, there is an app to count your life points but that is it.
8000
No. But if there is, it is probably already banned.
You can have as many life points as you want.
You beat him/her in a duel by reducing his/her life points to zero before they do.
8000. But in the anime the usually have either 2000 or 4000
No, Griggle only increases life, not decreases it.