Apart from creating a new Solution, which is necessary for any other activity, the order of the steps to follow is up to the user. However, the most common way is described below.
Start the engineering of one or more PLCs by creating a new Solution
Add one or more PLCs to the Solution
Assign platform parameters to the PLC
Add a communication channel to the PLC and set its communication parameters
Add communication elements to the channel
Add communication parameters to the elements
Create a project, add references
Create global variables, pam them on physical variables
Create a program in Fupla (in ST)
Define task(s) of the controller
Of course, do not forget to compile the solution every time the data structure changes (new variable, variable type change, new reference etc.).