I am easily distracted and can’t concentrate, how can I practice mindfulness??

You do not need to practice mindfulness, meditation, yoga, or whatsoever.
Meditation can help to relax the muscles but it can never help you achieve inner peace.
Inner peace is a subject of thoughts, how you perceive, process, and react to any circumstance.
For Inner peace, you need to do introspection, identify and acknowledge your sins, bad deeds, weaknesses, etc, listen to keertan for gyan, seek forgiveness, do seva, fight with your ego
ਬੰਦੇ ਖੋਜੁ ਦਿਲ ਹਰ ਰੋਜ ਨਾ ਫਿਰੁ ਪਰੇਸਾਨੀ ਮਾਹਿ ॥
This will clarify your mind with time. You will have many doubts but with time, you will find answers and your way of thinking and view points will change, and start to get aligned with SGGS.
You will then start approaching simplification and then Sunn Awastha, when all your mental affairs will get settled.
Then the stage will come:
ਜੋ ਨਰੁ ਦੁਖ ਮੈ ਦੁਖੁ ਨਹੀ ਮਾਨੈ ॥ਸੁਖ ਸਨੇਹੁ ਅਰੁ ਭੈ ਨਹੀ ਜਾ ਕੈ ਕੰਚਨ ਮਾਟੀ ਮਾਨੈ ॥….
When you get completely aligned with SGGS:
ਸਤਿਗੁਰ ਕੀ ਜਿਸ ਨੋ ਮਤਿ ਆਵੈ ਸੋ ਸਤਿਗੁਰ ਮਾਹਿ ਸਮਾਨਾ ||