Estimate your parking and/or transportation expenses for the plan year and enroll in the plan for that amount. The money is deducted pre-tax from each paycheck and is deposited into an account. Claims for expenses are submitted to the account and the reimbursement is issued to you accordingly.
You will have a period before the start of each plan year to enroll for these benefits – this is the Open Enrollment period. In some cases you may be allowed to join the plan mid year depending on your employers plan design.
A special feature of Section 132 benefits is the ability to have funds rollover from one plan year to the next. The rollover of funds would not occur until after the end of the claims run out period. Not all plans have a rollover, consult with the employer to see if your plan offers this feature.