Something pleasant is nice or enjoyable. Usually, a picnic in the park is considered a pleasant activity.
Pleasant is a word for things that are pleasing: ice cream is considered pleasant by most people. A second meaning refers to a person who is polite or agreeable. People who have good manners, give compliments, smile often are considered more pleasant than someone who screams and curses all the time. This word is often used for weather: clear skies and warm temperatures are signs of pleasant weather. Still, different weather (and other things) will be pleasant to different people.