There are many resources on the internet that will assist you in knowing what your child should by the time he enters kindegarten. The basics include counting 1-30, letter and letter sound recogntion, recognizing ones name, ect.
My son is 22 months old now. In teaching your child, repetition is the key for young children under five. At the age of 16 months my son could recognize all of the alphabet, identify and recite the sounds of all alphabet letters, recognize shapes, colors and count to 10 and recognize the numbers 1-10. (We are working on 11-20 now). I know that this sounds amazing, but true. Everyone was involved in this process from the babysitter to grandparents in reinforcing concepts.
For counting, we counted everything all day, going up and down stairs, his favorite toys, ect. We also purchased a book series from Brainy Baby with separate books for numbers, letters, shapes and the alphabet. The four book series had the same picture concepts throughout. We would read different books from the series on a daily basis. The books are very visually simulating and he enjoyed looking at the pictures. Buy this series if you can. It is geat!
For letter recognition, the Leap Frog video called "The Letter Factory" was great. We got it as a gift on his first birthday. He started watching the video in the evenings before bed at about thirteen or fourteen months. He really enjoyed and would cry when the video ended. By the time he was 16 months he would randomly identify letters and tell you the sounds of the letters as well. He now is the alphabet king! The video has catchy vinettes that for each letter and sound. We also reinforced the concepts identified in the video with our son. So we also recited the catchy songs for each letter and reinforced the visual concept given for each letter with him as he bathed, ate, walked or played in the park. Repetition was the key. Your son will LOVE this video.
Dom't worry too much that your child is not at the same level as other children at this point. Every child is different and have different learning curves. Tap into the things that your son enjoys doing and create learning opportunities from them.
Finally, make learning fun. Get excited about his grasp of anything. We would get excited about everything, which made our son want to get that positive response from us.
If you get the video and book series, please let me know how he likes it.