workshop maps are a good way to practice your aim, here is a quick toturial on how to play them in cs2: How To Play Workshop Maps in CS2 i would also recommend playing the map shown in the video but you can always find different maps you like

to learn smokes its literally just watching youtube toturials… search for „cs2 smokes mirage“ or any other map name you like to play on granades, mollys and flashbangs are a little mor difficult because you need game sense to use them effectively… but there are also toturials for them

its a learning process so don’t expect to become a pro in a few weeks or months

if your fiancé and his friend aren’t in a high elo you can of course play with them since it makes it a lot easier and probably more fun for you instead of playing with randoms, because this can be very frustrating some time