You are entitled to claim a deduction for some expenses that are directly related to earning your income.
These must be expenses that you paid for yourself and for which you weren't reimbursed, relate directly to earning your income, and you must have a record to prove it.
You can generally claim a deduction for the percentage of an expense which represents the portion of that expense that relates to you earning your income (this is to ensure you are not claiming expenses which are private in nature).
There are specific rules for different types of expenses, so it is important to check if the different types of expenses you have paid during the year are allowable deductions before you claim them in your income tax return.