Mind maps are saved on your device or a cloud of choice, such as Dropbox or iCloud Drive. You can make as many mind maps as you want. The free editions can save mind maps on your device only.

Mac or Windows
Each time you create a new document, you name it and choose where to save it — for example on your desktop or in a folder. If you choose to save the mind map in a cloud folder, such as Dropbox or iCloud Drive, the cloud app syncs the changes with the cloud.
Make sure to install the cloud app from the cloud's website first, unless you use iCloud Drive.

Mac: When using iCloud Drive and SimpleMind Pro for iPhone&iPad, save mind maps in the SimpleMind folder created by SimpleMind for iPad&iPhone (the folder with the SimpleMind icon). The reason is that SimpleMind is not allowed to access any files outside that one SimpleMind folder as a security measure by Apple.

iPad&iPhone
When you first start SimpleMind Pro or used in-app purchase, SimpleMind will ask if you want to use iCloud Drive. If you do, this will create a SimpleMind folder in iCloud Drive where mind maps will be saved. You can also use built-in clouds (such as Dropbox, Google Drive or NutStore) to sync your mind maps, see how to connect in this help.
Alternatively, store mind maps in any folder in Apple Files - meaning you can also store in a folder created by a cloud app. See how in this help.

Android
SimpleMind for Android can save mind maps on your device (Local) or in a built-in cloud: Dropbox, Google Drive and OneDrive. Mind maps saved in a cloud will be synced with that cloud.
See how to connect to a cloud.