Using a story book your child enjoys, read a sentence to them while they follow along with their finger. Take longer pauses than usual between words. Show them that the pauses actually take place as the gaps between the words appear. As you read, show them that at the start of every sentence there is a capital letter. At the end of every sentence there is a punctuation mark.
Read a newspaper to your child. Pause a bit longer between the words and point out the gaps. This can work as well with a magazine.
Have your child write their name down on a piece of paper. Now do the same except this time write it five times in a row without any spaces in between them. Ask your child if they can read their name. They should be able to but it would be more difficult. Explain to them that spaces help when reading words. They are especially needed when there is a group of words (sentences).
Explain that a sentence relays information. A group of words does not make up a sentence ( the the the the )