Communicate Your Resignation To Your Manager 1st (preferably)

The official way of announcing your resignation is usually in writing. This will usually be specified in your job contract, however, you can take it as standard practise to communicate your intention to leave in writing.

An email to your manager should be sufficient unless there are other HR requirements in the organisation.

Very important - don’t verbally share the news with anyone within the company until you have communicated it officially. It can send mixed signals if your manager hears it from other means. Best it comes from you directly.