An office action (also called an examination report) is a statement provided by an examining attorney where they notify the applicant and/or the applicant's legal representative of deficiencies within the filed trademark application.
The issuance of an office action does not immediately stop the trademark registration process and, depending on the proposed issue, can be overcome. The examining attorney will provide context and justification regarding their ruling based on the current trademark guidelines of the respective intellectual property office, together with providing the necessary steps to overcome the issue stated. The applicant or the applicant's legal representative will then have a choice of whether they would like to reply to the office action or not act at all. Failure to respond to an office action will result in the trademark application being abandoned.
If you file a trademark and receive an office action, you should be informed about the fact by your legal representative. If you don't have one, the IPO should inform you directly. Be aware of the deadline for responding.