Hello Melina!
First of all, all these words are in accussative case.
The words τον/την/το and το/τη/το can be the definite article or some times the weak forms of personal pronouns. Τον is for male , την for female , το for neutral. How can we distinguish them? They are articles when a noun (or adjective) follows : τον αδερφό μου. And because they are in accussative they are used usually as the object to the verb.
And they are personal pronouns when a verb follows: το έχω (i got it).
The words το/τη are the article again , in accussative, without the final - ν. When we use the final - ν? When the next word starts with : a vowel and κ, π, τ, μπ, ντ, γκ, τσ, τζ, ψ, ξ. example: Αγαπάω τον πατέρα μου( I love my father). But : Αγαπάω το γιο μου.( I love my son).
Other examples:
τη βάρκα, την ψεύτρα,
την αδερφή
το παιδί , τον μπαμπά, τη μητέρα etc
Now for the words : στον/στην/στο, στο/στη/στο
the preposition σε + τον, την , το (or το, τη ,το / depends on the next word if we use the final - ν or not) and they are used to declare the place (as I can remember now). Example: Θα πάω στο σχολείο. (I going to school).
ATTENTION: When the next word is male we must use στον , for female στην and for neutral στο. Examples: στο δρόμο(m), στην αγορά(f), στο σινεμά(n)
I hope you could understand my english!
XXX
Alexandra