Hi Isabel!
Nice to meet you! My name is Helga and I’m from Guatemala. I’m a native Spanish speaker and I’ll be glad to explain you in a very easy and fun when to use those pronouns. They act like direct and indirect object.
For example:
1. Hay que leerlos.
2. Lo tengo.
3. Cómelo en la escuela.
You have to use the questions,
Who is going to do the action (verb)? Or
What is the person going to do?
If you have any questions, please, don’t hesitate to contact me :)
Best wishes,
Helga Stolz