Bob did an excellent job providing enough examples of how "тебе" (Dative) and "тебя"(both Genitive and Accusative) are used in speech.

Another helpful way to see the difference between these two forms of the Personal Pronoun "ты" would be to familiarize yourself with the main functions of each of the six Cases, just like it-ogo advised. E.g.:

The Genitive Case expresses absence:
Я сказала, что ТЕБЯ нет дома.

The Accusative Case indicates the direct object (= focus, recipient) of the action that is named by a transitive verb:
Я вижу ТЕБЯ.
Я слышу ТЕБЯ.
Поздравляю ТЕБЯ с Днем Рождения!
Как я ТЕБЯ найду/узнаю?
Я люблю ТЕБЯ.


The Dative Case indicates the indirect object of the verb, usually it is a person who receives something named by the direct object:
Что мама подарила ТЕБЕ?
Я принесла ТЕБЕ (indirect object) цветы (direct object).
Я расскажу ТЕБЕ (indirect object) все новости (direct object).
Or in Bob's example:
Я покажу ТЕБЕ (indirect object) моих родителей (direct object).

Blessings in mastering Russian!