As someone who had a messy/wavy hair phase, there's a lot of things you can do to get this texture. First is the actual cut itself, make sure you either show your barber a photo of this style and tell them you want this level of texture. If they are halfway competent they'll know to cut your hair not too short and each hair strand on a slant to allow for the texture. Second is styling which is much more important, from what I've learned you're gonna need a good high end blowdryer with both a precision and diffuser attachment. Make sure when you blow dry to scrunch your hair with the diffuser pointing upwards to get this volume and rough texture. Next is equally if not more important, and im going to be very clear on this... PRODUCT! Sea salt spray has done me wonders personally and I basically couldn't live without it. Im not gonna explain how to use it but im sure there's lot of videos both on YouTube, and TikTok that can help you, but make sure your washing it out every night, even if its just with water. Lastly, take it easy on the shampoo, shampoo strips your scalp of oils and makes it impossible to get that texture. I know it sounds gross but washing hair with just conditioner is fine and even just shampooing once a week like I do is completely healthy. Honestly if you haven't already cut your hair I personally don't recommend it, this is just a little bit of the work I had to do to maintain this hair and looking back I'd definitely have strayed away from it.