What sort of work does a computer and information systems manager do?

The work this type of manager does depends on what the organization does. I worked at an insurance company as a Release Engineer my manager's organization consisted of the following teams--Release Engineering, Security Management, Data Base Management, Disaster Control, Larger organizations would split these teams between a number of managers.

I worked in Information Technology for many years and never wanted to become a manager. There are many tasks a manager has to do these days that are not related to technical skills--working with Human Resources for pay raises, grading performances, hiring and firing employees; attending long meetings; defining the budget for the teams; taking on new work and removing old work. So a manager gets away from technology for most of the day. The teams are the technology experts.

I worked for other companies when my manager managed completely different teams and I performed completely different tasks.

I'm not familiar with the exact title "computer and information systems manager", but I'm a Systems Engineer, and my manager is the Systems Engineering Manager, so I figure I'll take a swing at this. :)

First of all, "computer and information systems" can mean lots of things depending on the industry and/or field you work in. In some cases it might mean engineering tools for the personal computers of employees or customers (we call this "end point engineering" where I work). However I would say the most common use of the term applies to servers and network infrastructure—either on-premise or in the cloud (i.e. in data centers maintained by a provider like AWS, Azure, Google Cloud, etc.)—so that's the meaning I'll use here.

At my job, for example, I spend lots of time thinking about, building, and maintaining cloud infrastructure. In a literal sense this means writing a special kind of code that can be evaluated by a program that makes API calls to those cloud providers to do things—provision servers, configure compute hosts, and provision or modify network architecture. [1] Sometimes I also need to use web consoles to check things and verify the work being done. When I'm not doing that, I may be working on compute architecture designs, attending project meetings, or reading about topics relevant to our industry (there's lots of reading involved, as the tools and technology we use change so rapidly).

I'm not sure if your interest is specifically in being a manager, but there are lots of routes to get there. The best managers I know (whether they're "people managers" or "project managers") are folks with a solid background in systems engineering, software engineering, etc., so I'd encourage you to pursue that if you have management in mind for your future, and you'll be set up well to get there.

[1] See https://www.terraform.io for more information about this.

I would recommend focusing on an entry level position in IT first. Once you've worked in a Dev, sysadmin, network admin role you'll understand what a mgr does, and have the appropriate background to work on moving into that role. In an IS/IT MGMT role you'll be managing these professionals and ensuring delivery of software and services, so it's important to understand what they do and what challenges arise.