"Someone's walking towards here."
Translation:Biri buraya doğru yürüyor.
English can be a little sloppy here, and both have some exceptions, but "kimse" is used wherever the pronoun is indefinite (somebody, anybody, nobody) and "biri" where it is definite (someone in particular, a particular individual). Either can be used with a negative, but it is more common for kimse.
Nobody is coming - hic kimse geliyor
Someone is not coming - biri gelmiyor
Koran, i found that site about words' order: https://en.wikipedia.org/wiki/Turkish_grammar#Word_order. It explains how words'order can be modified and with what aim (objective).