1. If Nam go to bed late, he will be tired.
2. There are four tables in my room.

1. Nam goes to bed late, so he will be tired.
=> If Nam doesn't go to bed late, he won't be tired.
2. My room has four tables.
=> There are four tables in my room.
3. He has enough time, so he walks to school.
=> If he doesn't have enough time, he doesn't walk to school.