Magisk Manager is not capable by itself to grant us root privileges. This process is different for each device and must be done before the installation of Magisk Manager. Although it is closely related to the rooting world, this application fulfills other functions. Magisk Manager is a tool that acts as a manager of superuser permissions.
Most of the time, to root a device with Android, major changes must be made to sensitive partitions on the storage system. Also, it is necessary to unlock the bootloader, or boot manager. This, in many cases, can invalidate the manufacturer's warranty. If you are determined to do this, make sure you know your device model and look for information on how to obtain superuser privileges.
If your device already has root access, Magisk Manager is an indispensable tool to manage the applications that make use of that privilege. However, this application goes a little further and offers some very interesting features. For example, Magisk Manager can hide to specific applications that a device has been routed. So you can use those applications that usually do not work on a modified device such as your bank app or Pokemon Go. Additionally, it has a module installer that will help you apply deeper customization to the device. Finally, it lets you modify system files, including those with read-only permissions.
In short, Magisk Manager is the application you need after your device has been rooted. Keep in mind that both the process of rooting and the use of this tool can have serious consequences for your device, leaving it unusable in extreme cases. Therefore, be careful and modify your operating system only if you have the proper knowledge.