In order to benefit from the European Health Insurance Card (EHIC) that you obtained in your home country, you must first register with a 'Mutualité' (a medical insurance company).
The various Belgian 'Mutualités' or 'Mutuelles' are listed in the Yellow Pages.
You need to take your Health Card with you when registering. Afterwards, you can seek partial reimbursement for medical expenses directly from the Mutualité. Always take your EHIC with you when you consult a doctor/dentist or purchase prescribed medicines.
Obtain a receipt for all medical treatment or expenses.
You will need to submit original receipts when applying for reimbursements. In Belgium, around 75% of the cost of treatments and approved medicines will be refunded by your Mutualité.