You need to use the `docker exec` command with the ID or name of your container and the command itself that you want to run. Here’s a generic example:
```
docker exec -it container_name_or_id command_to_run
```
For instance, if you want to open a bash session in a running container (let’s say its ID is abc123), you would run this:
```
docker exec -it abc123 bash
```
Here `-it` is an option that allows you to interact with the container. `-i` stands for interactive, and `-t` attaches a pseudo-TTY.
