Hitman 2 is a pretty involved game because it takes time to fully explore each area. It is a game full of replayability and a ton of missions to complete. Each area can be played over and over because of all the different ways to complete the missions. The main part of each area is the option to play Mission Stories. Each mission has a certain number of them and here is how you find and start them.
How to follow Mission Stories
There are 2 ways to follow each Mission Story, and the first one is accessed through the menu before you start the mission. Just click on the Mission Stories tab and click follow on the one you want to do. You might even be able to do a couple in each mission because there are multiple for each of the targets. The second way is in the mission itself. Just open up the map tab and there is another Mission Story tab for you to change the one you are currently following.
How to locate the mission stories
It is actually really easy to find each of the missions. Once you are following a mission, you can then join the mission and there will be a little waypoint with a light bulb at the location you need to go to start the mission story. Once you initially listen or read whatever the start of the mission is, you will then receive the next instruction from the game. It will sort of walk you right through the mission so don't worry about second-guessing.
Go to the waypoint
It is pretty simple, once you get to the waypoint, the game will guide you through the mission like I said before. The game will not tell you everything because you might need to have something extra so make sure you have everything you need before going all the way through the mission. If it takes replaying it multiple times to master it, then that is what you should do.