How do you lose life? (Im a noob)

[Alegottu]

I just start playing Magic: the Gathering, and i have no idea how you lose life. Also, can you pick anything from your own library or do you have to pick your cards from the top or bottom of your library.

[The1337Magician]

You lose life due to your opponents actions. Whether it be their creatures attacking or a spell they play.
When you draw a card, you must take the top card of your deck (library) into your hand.

[The1337Magician]

Any other questions? I'm happy to answer anything about Magic.

[Gorzo]

Make sure to read the basic rule book, it is a good start for new players. I also advocate watching these videos here:

http://www.wizards.com/magic/tcg/newtomagic.aspx?x=mtg/tcg/newtomagic/learntoplay

I watched them when I first started playing, and they really helped me understand the basics a lot easier.

[The1337Magician]

Also, if you have time and spare money, you can buy one of the Duels of the Planeswalkers games for Xbox, Ps3, PC, or iPad. They are very good at teaching game basics and it easily keeps track of life totals and all the variables in the game. I hope we've been a help to you and I hope that you enjoy the game of Magic.

[Birdbrain]

Some spells you play deal damage to you. And some card cause you to pay life as a cost as well

[Paraluke]

Basically to answer your questions, cards that say "deal 2 damage to player" will make you lose life if you did not prevent it.

Creatures that attack you and left unblocked will deal combat damage to you equal to their power will make you lose life if you did not prevent it. (Read up on trample for another case when combat damage still hurts a player in spite of a blocker assigned to the creature)

Cards that say "player lose 2 life" will make you lose life and that loss cannot be prevented.

[Draxilion]

Cards that say "player lose 2 life" will make you lose life and that loss cannot be prevented.

. That's not entirely true it can be redirected as in the case of {redirect} and {palisade giant}

[Paraluke]

Lose life is usually not preventable. {Palisade giant} only redirects damage.

Redirect spell works on effects that target.  {Debt to the Deathless} makes  {Redirect} useless.