Don't panic if your child hasn't mastered all 26 letters and sounds. Kindergarten spends a huge portion of time working on letters, letter recognition, and letter and sound connection. But as your child enters he should at the very least "know" the alphabet song. The song itself is fun for children and it will help him to feel less confused when he begins his education. Knowing the song doesn't mean that your child has an understanding of the letters, but he will at least be familiar with the names. Practice singing it daily; children are masters at remembering songs, so he'll pick it up quickly.
Ideally children should be able to know some of the names of the letters, especially the first letter of their names. It isn't a requirement to enter kindergarten but it will help your child to be prepared for the lessons that are to come. A helpful tool to help her recognize letters is to display her name around the house; use wooden blocks or letter magnets which are inexpensive and educational.
Read to your child for at least twenty minutes every day. This simple act will help your child better understand letter names and letter sound recognition. Choose books that focus on letters like Dr. Seuss's "ABC: An Amazing Alphabet Book." As you read, ask your child to point out the names of letters, provide the sounds for some of them, and point out the names of letters. Don't worry if he doesn't know them all right away, it is the act that is important. These are all questions that will be asked of him when he enters school. It will help him to feel more prepared.
Remember that learning the alphabet is very confusing for children and it takes a lot of time. Don't try pushing the lessons on your child one month prior to starting school: you'll only confuse her more. It takes at least a year of instruction for a child to learn these skills and these skills vary from child to child. If your child is already entering kindergarten and doesn't know the alphabet, that's okay too. Just try singing the alphabet song together and work with her at home once school has started.