How to more easily update the project on the prod server from the dev server?

Question

git

There is a dev-server on which an empty --bare repository was created and the project was uploaded from the local machine via commit / push, a post-update hook was created that pulls in the dev-server directory under apache, after push from local machines, and then handles on prod.
It turns out that each local machine with a clone creates its own branch (under the task), commits and pushes its branch to the repository.

1. Do I need to merge branches before pushing or is it better to merge branches already on the dev server?
   
2. If everything is ok on dev, then it's time to upload to prod, is it worth uploading by hand or on the prod server to demolish the project files (demolish the project) and clone and update via pull?
   

I understand that you need to initially do it right, run tests and upload to prod, and once again there are a lot of projects, they are different, you need different conditions, and there are already containers (lxc), etc. But now at least to establish work with the git.

Answer 1

How do you launch a project? with the master branch or the left?
Usually merzhat in the master.
If everything is ok, then shoot for prod. Why hands? file a tool, a script that will do it himself.
In jenkins, in my opinion, there is a button right in the web muzzle, by which you can build and upload to prod (dev, stage)