The most popular Tool for MIUI to customize youre Phone in many diffrent Ways created by BurgerZ , it is the non-official version of Xposed for MIUI.
In WSM Tools you can Download many Module's (Apps)
and also Xposed modules what makes modding and theming easy for every budy.
To start with it install WSM Tools and don't forget to enable Root rights in the permissions App:
start the App > Type on Framework > Than hit install > reboot!
If you are finished with this open WSM Tools and select and an Module on the Online tab and install it. Now you have to activate your downloaded Module and set it up to. Then reboot and Changes become active.
( becarefull with xposed Modules because they are not official for MIUI and can caused problems!)
You can Download the Module on the XDA Thread by BalcanGSM