The construction ir + a + infinitive is used to express future:
Voy a llamar a mi madre = I am going to call my mom / I will
call my mom
It´s hard to distinguish between English be going to and will:
Ahora voy a llamar a mi madre – I´m going to call my mom now
Mañana voy a llamar a mi madre – Tomorrow I´ll call my mom
If you are speaking about a future fact that wil occur certainly, you can use
Present instead:
Mañana tenemos una clase de español – Tomorrow we are going to
have a Spanish lesson (certainly)