This is the first time that I am using Taxtron to file my taxes. How do I ensure that I cover all my income, expenses and claimed all my deductions?

You can switch to 'Steps' mode. You will be prompted through multiple steps where you will be asked to check the boxes that are applicable to you (if you have a T4, you will have to check the box for 'I was an Employee' in the 'Income' step), and asked to enter the related information. This will cover any information that needs to be reported on your tax return.