Maillotpois lays it out very clearly and succinctly. My very first race was in the rain on the first truly slick road tires. They were made by Avocet and all the bike shops folks asked me before the race for a post race report because no-tread road tires were a new thing. Gave me lots of confidence in them, of course.
Not only was it raining but it was the annual tomato harvest and I had never ridden in the rain. Think racing through tomato sauce.
I did fine by doing exactly what MP describes. I fished tailed in one corner but didn't panic and kept pedalling. You weigh so much more than the bike that it will follow the momentum of your body so if you can keep it going straight, the bike will straighten up.
I even survived the jerks who threw broken glass out on the road right in front of me. Never had that happen before or since. Amazing the effort people will put into being obnoxious.
Frends know gud humors when dey is hear it. ~ Da Crockydiles of ZZE.