すでに決まっている予定には am/is/are going to を使います。going to のあとには動詞の原形を続けます。（I'm ＝ I am です。）
I'm going to study
I'm going to study tonight.
I'm going to call Amina later.
We're going to eat at the cafe on Moffen Street.
やってみよう: ___ study tonight. (I'm going to / I going to / I'm go to) 答え: I'm going to — going to の前には am が必要です：I'm going to study。（I'm ＝ I am です。）am を落としたり、"going to" の形を変えたりしないようにしましょう。
am、is、それとも are？
I には am、he / she / it には is、you / we / they には are を使います。
I'm going to help.
Hiroshi is going to visit Senfarren.
They are going to stay.
Not "He are going to come." — say "He is going to come.". he, she, it には are ではなく is を使います。
やってみよう: Hiroshi ___ visit Senfarren. (is going to / are going to / going to) 答え: is going to — Hiroshi は1人（he）なので、is を使って is going to visit とします。（"are" は you, we, they 用です。）
動詞は原形のまま
going to のあとでは、動詞は原形のままです。-s も -ing もつけません。
She is going to study.
He is going to come at six.
They are going to play in the park.
Not "He is going to studies." — say "He is going to study.". going to のあとには動詞の原形を使います：studies ではなく study になります。
やってみよう: She is ___ tonight. (going to study / going to studies / going to studying) 答え: going to study — going to のあとでは、動詞は原形のまま使います：study。「studies」や「studying」にはしません。
to を忘れない
to をしっかり入れましょう：I'm going to study。省略してはいけません。
I'm going to visit Amina.
We're going to eat soon.
He's going to play later.
やってみよう: I'm ___ Amina on Saturday. (going to visit / going visit) 答え: going to visit — to を忘れないようにしましょう：going to visit。（「going visit」には to が抜けています。）
isn't / aren't going to
予定がないことを言うときは、am/is/are のあとに not を置きます。（isn't ＝ is not、aren't ＝ are not です。）
He isn't going to come.
We aren't going to stay.
He is not going to come. = He isn't going to come.
やってみよう: He ___ come tonight. (isn't going to / not going to / doesn't going to) 答え: isn't going to — is のあとに not を置きます：isn't going to come。（isn't ＝ is not です。）going to と一緒に "doesn't" は使いません。
疑問文の作り方
質問するときは、Am / Is / Are を文頭に置きます：Are you going to...? Is he going to...?
Are you going to study?
Is he going to come?
What are you going to do?
やってみよう: ___ study this weekend? (Are you going to / You are going to / Do you going to) 答え: Are you going to — 質問するときは Are を文頭に置きます：Are you going to study?。「You are going to」は伝える文であり質問ではありません。また「do」を足す必要もありません。
やってみよう: They ___ play in the park. (are going to / is going to / going to) 答え: are going to — 「They」には are を合わせます：are going to play。「going to」と動詞の原形を使いましょう。