A scalar is a quantity that only has magnitude. Some examples include mass, temperature, and energy. These can be expressed with simple numbers and units like 3 grams or 42 degrees Fahrenheit.
Other quantities need more information to be fully descriptive or precise. For example, forces. If I ask a question like, “I will apply a force of 2 pounds on this rock, what will happen to the rock?” That is a difficult question to answer. You will say, “Well that depends on which direction you push.” And you would be right. The rock will respond in a variety of different ways depending on the direction in which the force is applied. That is why force is a vector quantity. Vectors have 2 aspects. They have magnitude AND direction and are typically represented by a line with an arrowhead at one end. The length of the line represents the magnitude according to some scale and the orientation of the line and the arrowhead show the direction. Other examples of vector quantities include velocity, momentum, and displacement.