If I press Command-H, an activated window disappear. How can I make it appear with shortcuts?
There is no shortcut to bring the window back, because the app loses focus when hidden. To bring its windows back, you have to give it focus again.
The easiest way to do this is with the cmd+tab shortcut. Press that, then leave cmd held down. You'll see the App Switcher:
From here, you can give focus to an app, as well as hide and show it without focusing.
To focus an app and show it's windows:
Open the app switcher, then (while still holding down cmd press tab until the darkened box is over the app you want to focus. Then, release the keys.
To show an app's windows without focusing:
Open the app switcher, then (while still holding down cmd press tab until the darkened box is over the app you want to focus. While still holding down cmd, press h Then, release the keys.
If you want to 'hide' one window and don't want the app to lose focus, you can minimize the window. Do that by clicking the green button at its top right, or using Window-> Mimize (cmd+m).
To restore a minimized window, click its name in the app's Window menu. Or, you can either click the window's icon in the right of your dock, or the app's Dock icon (depending on your settings).
You can simply use the task switcher ( ⌘ cmd + ⇥ tab ) to bring the application back into focus and display it normally.