Gitlab-CI and Pipelines: How to Trigger a Pipeline Based on a Merged Branch Event?

Hello,
First of all I hope I am writing to the correct group. Please redirect me if I am not.

We have a need to auto-deploy our projects to various server instances at the time their corresponding branches are merged back to the develop branch.

That is the use case I am uncertain how to address using gitlab and pipelines, etc. Since it is triggered by the merge event, I don’t know for sure how to 1) listen for those events, and 2) where/how to capture the steps (currently manual bash scripts0 to perform the deployment activities and post-deployment (e.g. starting containers, etc.) activities.

I am basically familiar with AutoDevOps, but I do not need anything to fancy for the time being. We are not using Kubernetes and my understanding is that you need Kubernetes for AutoDevOps.

I would grateful for any general or even specific guidance on how to proceed. thanks!