Cześć Luz!
Nie masz za co przepraszać! Jestem tu, żeby pomóc :)
I think you just gave me (unintentionally) a good idea for a new blog post, thank you :)
First of all, "się" is a reflexive pronoun – you use it whenever the action expressed by a given verb is directed at the person performing this action. If someone does something to him/herself, we use "się".
For example: Myję się - I wash myself
On się myje - he washes himself
Oni się czeszą - they comb themselves
The easy thing is that in Polish, się doesn't change with reflexive verbs, we always use it in this form, regardless of the subject of the sentence. However, się is also used with other verbs that are not usually reflexive in other language, such as uczyć się (to study), cieszyć się (to be glad), these need to be learned by heart :)
As for the other words, such as: mnie, ciebie, etc., these object pronouns - they tell us to whom something was done.
Lubię cię - I like you
Nie lubię go - I don't like him
Nie zjem ich - I won't eat them
As you can see, się is only used with specific kind of verbs and often (but not always) it is used in reflexive verbs, similar to the English self.
The other pronouns refer to other people, these are basically the case forms of the personal pronouns.
I hope it is clearer now. Please let me know if you need further explanations and more examples :)