You say the 'first year of school', so I'm not sure if your son is kindergarten or first grade. Unless he has trouble answering questions about what you read to him, I wouldn't worry about comprehension yet.
It's important to understand that learning to read is a process that has distinct stages. They go together something like this:
Skills for pre-literate or preparing readers
- identifying letters
- associating letters and sounds
- predicting text flow (left-to-right, top-to-bottom in English)
- recognizing that words are units of letters, and that spaces separate them
Skills for beginning readers
- hearing sound sequences in spoken language
- seeing the predictability of order of letters in words
- identifying initial sounds
- using visual information to figure out simple words (often nouns and high frequency 'sight' words are recognized first)
- one spoken word is one written word (1:1 correspondence), often demonstrated by pointing at words while reading
Skills for accelerating readers
- breaking words apart to figure them out (both with phonetics and common chunks like 'ing', 'ed', 's' that may be added to familiar words)
- using sentence structure and meaning to figure out words (does that word make sense there?)
- increasing reading fluency demonstrated by smooth reading of phrases and appropriate vocal expression in reading
- recognition of the implicit meaning of punctuation (stops, pauses, speech)
Your son won't demonstrate reading comprehension until he begins to accelerate, and it sounds like he is still working on some of his beginning skills. The best thing you can to do help him master those skills is to increase his volume of appropriately levelled texts and read with him. This will help him practice problem-solving new words, and build his confidence as he learns to see himself as a reader. He'll need to master those skills before he can really think about what he's reading.
Also, encouraging him to write (just a word or two, or let him dictate to you) will help reinforce the connection between sounds and letters, and start him down the path of using context and meaning to figure out unknown words. (Don't worry about the spelling as long as the idea is correct.)
When you start to hear a difference in his reading fluency, that's when you should expect that he is beginning to retain the information he is reading. You can encourage comprehension at that point by modelling retelling, summarizing stories, and making predictions about what might happen during a story (based on the pictures or even just the title).