how to floss and choice of floss

So my dentist suggested me to floss, which I almost never did. I know I definitely should. I started by search "how to floss" on youtube:

https://www.youtube.com/watch?v=WviE5aa5Ha0&t=151s

But I found it really difficult to floss the teeth as they go inside of my mouth. Also, I feel sour and ache when I'm flossing. Is this expected?

In the market I found two kinds of flosses:

https://preview.redd.it/4jn15c3wgevd1.jpg?width=1702&format=pjpg&auto=webp&s=dbcf7703e02c5f78d79d10fb5b26aa2478cb4bb2

https://preview.redd.it/lz90gd3wgevd1.jpg?width=1280&format=pjpg&auto=webp&s=a26597f16a6f255e2151d9c043b2dc910f067d1f

It seems that the second one is better at reaching all the gaps between teeth. Would they be equivalently good?

Sorry that my post is a little bit messy, but I'm really trying to get use to floss even though it's a little bit painful at first. Suggestions and maybe some encouragement would be highly appreciated, thanks!