The point of mindfulness is to bring your awareness to the present moment, and to stop focusing on the past and future.
Mindfulness practices include certain exercises that help achieve this goal, such as meditation, yoga, and being mindful during certain actions such as walking, brushing your teeth, reading, and basically any other action you perform.
To be mindful means to really pay close attention to even the small details of what is currently happening and going on. You can even be mindful while walking by focusing on how your heels feel when they hit the floor, and how your foot moves as you transition from heel to toe in each step.
You can be mindful in the gym, when lifting weights, by focusing on each muscle being activated by the exercise you are doing.
Mindfulness can be implemented in most actions you do on a daily basis, and their goal is to keep your mind in the present moment, focusing on the here and now, and preventing it from wandering off to unwanted thoughts such as the past and future.