I read many posts across a variety of internet fora (yes, forum is a neuter noun that becomes fora when in the plural form) and I am increasing annoyed with peoples' use of the language that they claim to be fluent in. I do accept from the outset that there are many people for whom (accusative) English is not their (showing ownership) first language and that it is quite difficult.
The "problem" with English is that it does not come from a single root; instead the language is derived from a Germanic root (Anglo-Saxon), Latin (both through the Roman invasion and the Bible being in Latin), Greek (again through the Bible and being used as a scholarly language as late as last century) as well as the influence of others like that native British, Vikings, Celts, Picts etc.
As a consequence you have a language that largely uniform how it deals with language rules but then there are always exceptions.
Common irritations
There, Their and They're
Quite simple to deal with
There - indicating a place, "There are thirty boyz in that mob"
Their - showing possession, "The boyz have got their killy axes ready"
They're - contraction of they are, "They're about to assault your fire warriors"
Its and It's
It's - this should be used most frequently, it is a contraction of "it is", "It's not fair you rolled 120 attack dice"
Its - this is a possessive pronoun, think would this make sense to use his or her in its place, "Its got a boss pole", in this case the "It" is the nob.