The bone stock basics are this:

Take a period of time during the day or several periods of time. I recommend honestly starting with 1 minute and then 5 minute chunks 4 times a day.

In that time you want to sit somewhere vaguely comfortable. Even your desk chair is fine.

Then focus on your breath. Find an aspect that you can focus on. Different aspects are easier fo different people.

Some like to focus on the feeling of the air passing through the nostrils on inhale or exhale.

Some focus on the feelings of the lungs filling and the ribs expanding.

Others focus on the entire cycle of breathing.

Then the final step is when you notice your attention wandering to anything at all, you label that "thinking" and move your attention back to your breath.

The point isn't to "Stop Thinking" the point is to notice your thoughts, feelings or emotions as they happen and stop following the narrative of the thought. Don't judge the thought. Don't indulge the thought.

Some also find it helpful to repeat "I am breathing in, I am breathing out, I am present." However as your practice goes on and evolves you should try stopping the mantra and just focusing on the breath.

Like any exercise you are working a muscle. It's going to be difficult at first and almost seem impossible.

Common complaints are,"I just keep getting off track!" Or "I catch myself daydreaming!"

Awesome. Great. That's literally the practice. Catching yourself and bringing your attention back is flexing the attention muscle.

I'm present this secularly and have plenty of information in that realm but this is, at it's core, a Buddhist practice for me and I'd be happy to expand on that as well.