Plastering is one of the most difficult of trades to master; it takes a great deal of skill but is also partly a black art; you must understand how the various plastering materials behave under different circumstances & then you need several years experience to perfect it. Googling will bring up many sites worth a look at & there are also videos available & short courses available which will at least teach you the basics. Hire a plasterer for the day, watch him at work & pick his brains; some will be quiet happy for you to watch & bend their ear but others will quickly tell you to bog off & leave them alone. We all had to start at the beginning & your first attempts are likely to be rather less than perfect or even disastrous but if you feel like having a go, start by practicing on some sheets of plasterboard, at least it will help with your trowel skills.
Generally you will find you can either do it or you can’t & some will never be any good no matter how many years they try. Have a look through the archive posts, there are many threads giving novice advice & some pretty ghastly photos of plastering attempts, some supposedly done by professionals.