docker attach will let you connect to your Docker container, but this isn't really the same thing as ssh. If your container is running a webserver, for example, docker attach will probably connect you to the stdout of the web server process. It won't necessarily give you a shell.
The docker exec command is probably what you are looking for; this will let you run arbitrary commands inside an existing container. For example, to run bash inside a container:
docker exec -it <mycontainer> sh

Of course, whatever command you are running must exist in the container filesystem; if your container doesn't have sh, this will fail with something like:
OCI runtime exec failed: exec failed: unable to start container process:
exec: "sh": executable file not found in $PATH: unknown

[If your container doesn't have sh -- which is a common case for minimal images -- you may need to investigate other ways to explore the container filesystem.]
In the above command <mycontainer> is the name or ID of the target container. It doesn't matter whether or not you're using docker compose; just run docker ps and use either the ID (a hexadecimal string displayed in the first column) or the name (displayed in the final column). E.g., given:
$ docker ps
d2d4a89aaee9        larsks/mini-httpd   "mini_httpd -d /cont   7 days ago          Up 7 days                               web                 

I can run:
$ docker exec -it web ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
18: eth0: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP 
    link/ether 02:42:ac:11:00:03 brd ff:ff:ff:ff:ff:ff
    inet 172.17.0.3/16 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::42:acff:fe11:3/64 scope link 
       valid_lft forever preferred_lft forever

I could accomplish the same thing by running:
$ docker exec -it d2d4a89aaee9 ip addr

Similarly, I could start a shell in the container;
$ docker exec -it web sh
/ # echo This is inside the container.
This is inside the container.
/ # exit
$
 In commands shown in this answer, the -i and -t options (combined as -it) are necessary to get an interactive shell:

-i keeps stdin connected; if you don't specify -i, the shell will simply exit.

-t allocates a tty device; if you don't specify -t, you won't have a very pleasant interactive experience (there will be no shell prompt or job control, for example).

 If you're specifically using docker compose, there is a convenience docker compose exec command that works very much like the docker exec command, except:

It defaults to the behavior of -i and -t
It allows you to refer to containers by their service name in your compose.yaml file.

For example, if you have a compose.yaml like this:
services:
  web:
    image: docker.io/alpinelinux/darkhttpd

Then you can run:
docker compose exec web sh

The equivalent docker exec command would be something like:
docker exec -it myproject-web-1 sh
 Page 2   I'm getting started working with Docker. I'm using the WordPress base image and docker-compose.
I'm trying to ssh into one of the containers to inspect the files/directories that were created during the initial build. I tried to run docker-compose run containername ls -la, but that didn't do anything. Even if it did, I'd rather have a console where I can traverse the directory structure, rather than run a single command. What is the right way to do this with Docker?   7