1) You can create it with set and get functions. They are nothing but two Simulink functions, where the output of the Set is connected to the input of the Get. When you want to assign a new value to this variable, you use the following code:
And when you want to query the variable, you can use:
For a counter, you first get the old value, increment it, and then set the new value.
2) You should create a Simulink function, which has a Digital Clock block in it. When you needed to get the simulation time, you simply use: