It is written Squier STRAT by Fender on the head but I can't figure out which series does it belong to. Body colors are black&white, neck is dark brown and head is light brown. How do I know if it's Affinity or Standard? If Affinity, how do I know if it's Fat Strat or just Strat?
A fat strat will have 1 humbucker pickup and 2 single coil pickups , as for the other maybe a squire owner could help, I cant.
did u get it from a store?
cause if u did and it was like 150 or 200 it is an affinity which suck ass and if u payed more then that its proly a stnadard which seeing as its a squir it sucks ass to and a fat has a bucker the other has the trio of singles
my gear:
Schecter Damien 6 w/emg's
gibson sg standard
dean performer e acou/elec
ibanez tone blaster=[
ibanez ts7 tubescreamer
boss ds-1
boss sd-1
dunlop crybaby from hell wah
Its an affinity. Standards say Squier STRATOCASTER, not STRAT.
Affinity is better to upgrade, it has worse pickups but better wood
Erm...affinity series say.."affinity" on the headstock.. pretty straight forward really.
I have played squire's that are good playing guitars . I have never owned one though and don't know about long term . There also some pro guitarists that do use them for some applications IE slide for the telecasters , so don't write them off , If it feels write to you ,go for it - but be cautious.
Hey man, i'm a guitar noob as well (will be buying my first electric and starting in about a month) and i have done A LOT of reasearch on various guitars!

In my case im getting a Squier Standard Fat Strat, the way to tell whether its a fat strat or standard strat is by the pickguard (the plastic thing on the body of the guitar), in both affinity and standard fat strats, the pickguard is black.

But if you know more about the technical bits and pieces of a guitar, another way to tell whether its a fat strat or standard is the pickups. On fat strats, if you look at the strumming area (bridge) the pickup arrangements are different to that of a standard strat.

Looking side onto the guitar the pickups on a fat strat look like this
( [] | | )==neck==> This is a typical HSS (humbucker, single, single) setup

Where as on a standard strat pickups look more like this
( / | | )==neck==> A typical 3 single coil setup

As for tellin whether its Affinity or Standard series, i guess you just have to look at the writing on the head stock, there should be some differences there.

Hope this helps!
I finally got my gear!

Squier Deluxe Series Satin Trans Double Fat Strat
Roland Cube 15