Everyone normally experiences anxiety. Worrying is a form of anxiety, as is nervousness. People have normal anxieties about all kinds of things: a coming review or exam, an illness or our health, our weight, our food, social gatherings with persons not well known, public speaking, financial uncertainties, the way we are disciplining our children, whether our children will turn out well, what we should do with our lives, etc., etc.
Anxiety is part of every life. If you have ever worried, fussed, hovered, feared, gotten butterflies in your stomach, or wanted to "run and hide", you have experienced anxiety.
Anxiety occurs on a continuum. It is abnormal to feel no anxiety. On the other end, it is abnormal to feel too much anxiety, or irrational anxiety.
But when you say, "I couldn't get exactly what anxiety is", it's because you're calling it something else. If you've ever been surprised (not in a good way) by a police car behind you turning on it's lights, or have been nervous about an approaching dog, worried you left the stove on, a window opened or the doors unlocked, have feared getting into trouble, worried about meeting your girlfriend's parents or felt uncomfortable walking in a bad neighborhood alone, then you know what anxiety is.
An anxiety disorder occurs when anxiety is so intense that it is interfering in some way with your normal life. But since you did not ask about anxiety disorders, I will leave it at that.