See on your tax (avis d'imposition) the different reference numbers (numéro fiscal, Référence de l'avis, etc) and the web site. It is rather straight-forward.
Follow this link here
Click on « Payer en ligne »
Numéro fiscal : enter your fiscal number which you will find on your income tax form or any other taxes
Click on “Payer en ligne”
Enter the reference number of the tax you are paying.
(référence de l’avis)You will have to enter your French bank details. Once the tax is paid you will receive an email confirming your payment. Keep it for your records.
Please note you won't be able to pay your tax online once you have missed the deadline.
More information here.
Please send me an email here if you require assistance with paying your taxe d'habitation online or after the deadline.