’Tis impossible to be sure of any thing but Death and Taxes - The Cobbler of Preston by Christopher Bullock (1716)
For foreigners declaring taxes in France for the first time, you will need to do it in person. Be careful, there is a deadline, which is different for online declarations versus offline ones.
Here are things you need to prepare:
1. Declaration Form : You can either: 1) download and print the form here: https://www.impots.gouv.fr/sites/default/files/formulaires/2042/2022/2042_3926.pdf or 2) go and queue at the tax offices near your place (Centre des Finances ou Centre des Finances Publique Services des Impots). Fill in the necessary fields accordingly.
2. Fiche de paie/Payslip : If you already have your social security number, you can access your payslip through ENSAP. However, there might be a chance that you did not have it yet, or the system hasn't update your social security number. In this case, contact the human resource office that hires you (ask Malika to ask them for you) in case they don't reply. You can trace back to the person who emailed you about signing your contract, this person should know who to approach. One you have your payslips for the year, have them in hardcopy.
3. (For first-time declarer) Tenant Agreement : Bring along a copy of your tenant agreement of where you stayed during the financial year in which you are declaring.
Once you have all these documents and filled in. Bring them to the tax office. You might need to queue. When it is your turn, just tell them you are declaring tax for the first time, they will know what to do. Then you are good to go. You can also just mail them in as a registered letter with an 'accusé de récéption'.
You will then receive the 'avis d'impot' in August of the year you declared your taxes. That will contain your 'numéro fiscale'. With this, you can create an account on https://www.impots.gouv.fr/accueil and do your later declaration of taxes online from the second time around.