how to check what is going on inside of docker container

root@ubuntu:~# docker ps

CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                              NAMES
0a41e947e925        wordpress:latest    "/entrypoint.sh apach"   10 minutes ago      Up 10 minutes       0.0.0.0:8000->80/tcp               wordpress_wordpress_1
8526889870a9        mysql:5.7           "docker-entrypoint.sh"   10 minutes ago      Up 10 minutes       3306/tcp                           wordpress_db_1
e01674b264b4        nginx               "nginx -g 'daemon off"   About an hour ago   Up 51 minutes       80/tcp, 443/tcp                    nginx_nginx_1
69581c420e2b        rancher/server      "/usr/bin/s6-svscan /"   12 hours ago        Up About an hour    3306/tcp, 0.0.0.0:8080->8080/tcp   silly_mclean

root@ubuntu:~# docker exec -it 0a41e947e925 /bin/bash

root@0a41e947e925:/var/www/html# ls
index.php    readme.html      wp-admin            wp-comments-post.php  wp-config.php  wp-cron.php  wp-links-opml.php  wp-login.php  wp-settings.php  wp-trackback.php
license.txt  wp-activate.php  wp-blog-header.php  wp-config-sample.php  wp-content     wp-includes  wp-load.php        wp-mail.php   wp-signup.php    xmlrpc.php