Ok I am pretty experienced in this field, and i can say there is no easy way to learn how to run or parkour or trick. Its practice. Now what i can help with is learning to balance your tori to continue a run or gain momentum. What i think of my arms of, are as weights used to counter offset balancing.
Now what i usually dont do is ever touch my chest unless im relaxing it to start a jump. You want to work with your lumbar and pecs. Never contract the pec of the current stepping leg. That is a sure fire way to fuck up your balance and flow and continue to not learn properly.
Now remember this is no easy way to learn to freerun, but you can make it easier by ditching the youtube run and trying to learn a custom run. You can use the youtube run format but change up certain things. The youtube run doesnt work forever. I have learned 3 custom runs i have made up myself that i am willing to share with anyone interested in them.
Now all in all i can say that to learn free running, focus on learning how to balance your tori, then try to string in a running motion. Then from that add in turns and such.
Hope i helped someone <3