Magic, Spell drain Options

[santeria]

Howdy, I am very new to shadowrun but I have read most of 3rd Ed Basebook, Magic in the Shadows, and Man and Machine, and there is 1 thing I don't really understand, spell drain.

I see how +1(M) is just half the force of the spell plus 1 and moderate, but the thing that throws me off is when there is a +1 or +2 inside the ().

And another thing, So I choose the force that I cast a spell for all spells? In the descripion of some they say what the force limits on the spell and so forth but on some it doesn't say anything about it at all, so why would't people for those spells always use just 1 force to take less drain? Unless I totally read everything wrong it doesnt make much sense. :( Thanks.

BTW is there a newbie or help subforum on here? I didn't see one. Thanks again.