Question

Particle help (Japanese).

Answer 1

1. What particle shall I use? メリーさんは、トムさん＿　てがみを　かきました。

Mary wrote a letter to Tom.

を
に
が
と

2. What particle shall I use? ロバートさんは　アリシアさんに　でんわ＿します。

Robert calls Alicia.

を
に
が
と

Answer 2

@Opcode
Can you explain particles I don't understand them at all

Answer 3

を is for the object of the verb
に is for the destination or the "destinee" (I mean the one that receives something). It can be translated by "to"
が is for the grammatical subject of the verb
と is "with" (you will learn later that it also introduces some subordinate clauses like "I think 'that'...)

Answer 4

メリーさんは、トムさん(を) 　てがみを　かきました。

ロバートさんは　アリシアさんに　でんわ(を)します。

Answer 5

The second one is ok, but in the first one, Tom is the one who receives the letter.
"Mary wrote a letter TO Tom". so you should use the particle for destination に.

Answer 6

When using the verb 'to give' あげます, use を for the object and に　for the receiver.