Inference means using the clues in the text to discover what is NOT directly stated.
For example, read the short passage below and I will tell you how to make an inference.
Ana collected shells. Then she went for a swim in the cool, salty water.
Explicitly, which means things are stated clearly and in detail, I know that Ana collected shells, she went for a swim, and that the water was cool and salty. Implicitly, which means things are not clearly expressed and that I have to read between the lines as Mr. Bruce always tells us and he tells us we have to dig deeper to find the meaning. I know that Ana is probably at the ocean.
I know this because in the passage it says that the water is salty. That is how you make an inference.