This kind of question is very frustrating, because there is simply not enough information to provide a reasonable answer.
First, read the tutorial Learn PLCs at the top of the page. It will give you a basic idea about the way PLCs work.
To proceed you need to break the project into steps. You need to first of all write a description of the process, what is being controlled, what the basis of the control is, and what is going to dictate the sequence of operations and the machine.
Then you need to create an input/output list that identifies all of the sensors and switches read by the PLC inputs and all of the relays, drives, and devices controlled by the output.
Then you need to break the logic into steps, writing down the sequence for each control loop in plain language. You need to identify the adjustments to be made by the operator, like time delay ssettings etc. and how they will be entered. You need to identify the alarms that will be created, and the action to be taken by the PLC if they occur.
Then you can begin to write your logic. Don't try to do it all in your head in advance. Simply start writing the ladder logic using your description as a guide. Take it one step at a time. As you add new rungs you will probably need to go back and revise the logic already written as new ineractions and new ideas occur to you.
