Here is an easy way to know for beginners. Check to see if you experience any one of the followings in your one breath: Your breath becomes long or deep on its own. Your body becomes relaxed. Your mind becomes calm.
No need to think anything.
If you are aware of your breath, you are knowing the physical sensations of your breath that are constantly changing from moment to moment in the present. Otherwise you are thinking about breath, for example, remembering your breath that happened in the past or imagining about a breath.
Learn from distractions such as mental chatters or sounds, especially when you can not avoid them. They will become your good teachers. However, they are useless and become distractions to you when you do not know how to learn from them.
When you do it in a way that is difficult, it is difficult.
When you are thinking about the future, know that you are thinking.
Use a right meditation technique correctly.
When you simply do nothing, thoughts will stop on their own. When you clearly notice your breath, thoughts will also stop. There are more effective and lasting ways of achieving it. For example, knowing the true nature of the thoughts or making your mind happy & healthy.
Mindfulness refers to being aware of something. Mindfulness also refers to the capacity of the mind for knowing. Mindfulness can also refer to other things and can be interpreted in various different ways. If you wish to know mindfulness, it’s best to try mindfulness practice for yourself.