The definition of inferences is to guess based on somebody's words, body movements, and face looks. On different circumstances like reading a book, use a dictionary to look up adjective words you don't know.
One example from Teen Ink is: "My school has began a new campaign against bullying, so there have been anti-bullying posters plastered all over the walls of the school like the ugly wall-paper on the walls of my grandma's living room." I can infer from this is that the author is is that he/she is either proud to explain this new campaign and that he/she may not like the ugly wall-paper.
Another example from Teen Ink is: "The second thing the posters say is to make friends. With who, the bully? Or make friends with other people so the bully won't bother you anymore? In case the school hasn't noticed bullies, as annoying and unpleasent as they are, also have friends. That means now the bully and their friends can now bully you and your friends!"