"W.T.F's a function lock?"
Most laptops have keys that perform multiple functions (such as adjusting the brightness of the screen). These additional functions are usually (but not always) marked on the keys in blue. There is usually one extra key, labelled "Fn", which allows you to access the additional functions. On some laptops, you need to press and hold it when accessing the additional functions, on others it works like the caps-lock (ie - you press once to engage it, and again to disengage it). In such cases, it's called the function lock.