Children first learn to talk about now, here, this very moment.
I spend a lot of time helping parents move into the present moment mentally and talk about here, now, this very moment.
If your child is just beginning to talk, you can help your child the most by talking about the interesting things that are going on in front of your child moment-by-moment. If there is a dog, eighteen inches from your child, talk about that dog and not the dog at grandma's house who looks like that dog. Don't even talk about the bone in the refrigerator until the bone is in your hand or the dog's mouth.
At some point, though, your child will master the language of now and start to learn the mental trick of thinking about the past and thinking about the future. At that point, there are about a thousand language skills that he or she will need to learn in order to tell you what happened at school today. Even more language skills are needed to explain what he or she wants to do at the playground this afternoon.
When your child is ready, use visual supports like the one pictured above. Take lots of digital photographs and organize these with your child, talking about different time frames in a way that makes sense to your child. Pictures are a bridge between now and the past or now and the future and make it easier for you to show your child how to tell stories, make plans, think about things that are not here and now. Pictures from your child's own life and lots of practice with you showing the way will help your child learn to talk about yesterday, today, and tomorrow.