は (Wa): Sets the overall topic of the sentence ("As for X...").
が (Ga): Identifies the specific subject or highlights new information.
を (O/Wo): Marks the direct object receiving an action (りんご を たべる).
に (Ni): Specific time (7時 に) or target / destination of motion.
で (De): Location where an action takes place (家 で たべる) or tool used.
へ (E/He): Direction toward a destination (日本 へ いく).
と (To): Exhaustive "and" connecting nouns (A と B) or "with".