1. Attaching DO / IDO Pronouns
As you know, direct object and indirect object pronouns go in front of the conjugated verb.
EX: Me lo darás mañana?
Will you give it to me tomorrow?
But… what if there are 2 verbs? The direct object and indirect object pronouns may still go in front of the conjugated verb…
EX: Sí, te lo voy a dar mañana.
Yes, I am going to give it to you tomorrow.
OR…. Do you remember the other way???

2. OR: Sí, voy a dartelo mañana.
The direct and indirect object pronouns may be attached to the infinitive (2nd verb). EX: Sí te lo voy a dar mañana. Yes, I am going to give it to you tomorrow.
OR:
Sí, voy a dartelo mañana.
When this is done, you must add an accent mark to maintain correct pronunciation.
But wait!
There’s a trick!
Just add the accent mark on the 3rd from last vowel. Done!
Remember to keep the same order as before: ID

3. Examples:
They are going to give it to us. OR I am going to tell it to you. We are going to write them for her.
Nos lo van a dar.
Van a dárnoslo.
Te lo voy a decir.
Voy a decírtelo.
Se los vamos a escribir.
Vamos a escribírselos.

4. Practice
She is going to give it to them. OR You are going to tell it to her. I am going to buy it for you.
(Ella) se lo va a dar a ellos.
(Ella) va a dárselo a ellos.
(Tu) se lo vas a decir a ella.
(Tu) vas a decírselo a ella.
(Yo) te lo voy a comprar.
(Yo) voy a comprártelo.