My two main problems with CS:GO (yeah that's my first CS) when I started playing it were: 1) no ironsights except snipers and 2) no melee attack except the knife.
Having spent most of my 10 years of shooter experience with Red Orchestra, CoD series and several hours on Battlefield Bad Company 2, I had a huge problem with the absence of ironsights for the guns except the snipers. I am not a sniper fanboy, with rare exceptions I use the unscoped ones or if there is holographic, red dot and at rare occasions an acog, still those are no sniper scopes. RO2/RS mostly features me with an unscoped bolt-action or semi-auto. So CS:GO placed quite some challenge for me with its no sights policy. I have watched several tutorials to accommodate to the crosshairs only.
The second thing is, that I am used to insta-melee by clicking my right mouse button (ADS is pressing mousewheel), so CS:GO left me stranded there again as I was in close quarters and tried to thrust my buttstock into the enemy, but nothing happened, except me dying to their knives. I learned this one far quicker though than the no sights issue. I simply mapped the knive drawing to my thumb mouse button.
The posted videos are informative and easy to understand, hopefully they will help improve in CS:GO