File menu > Save
Keyboard > CTRL+S
Save updates the current scene by overwriting the last save of the scene. If no scene was previously saved, this command works like Save As.
See also
Interface
When you save a scene, you save the system settings also. When you open the file again, it is opened with the same viewport configuration, view and zoom levels, snap and grid settings, and so on.
The software allows you to incrementally number saved files and to make automatic backup files at specified time intervals. The options to set up Increment on Save and Backup on Save are in the Files panel of the Preference Settings dialog.