A permission set is a collection of settings and permissions that give users access to various tools and functions. One profile can be assigned per user whereas we can assign multiple permission sets to the user. We can give the users desired permissions without changing the profiles.
Create Permission Set
Setup > Manager Users > Permission Sets > New
Enter Label and API Name (Auto Populates)
User Licenses: If you to assign permission set to various users with different user licenses select “None”. If you want to assign permission set to specified license user then select user license.
A permission set's overview page provides an entry point for all of the permissions in a permission set. Under Apps and System, click any of the links to view or edit permissions and settings.
Click System Permission
System Permission > Edit (Enable Customize Application) > Save
Assign permission set to the desired user.
Manage Users > Users > (Select Desired User> Permission Set Assignments (Edit Assignments)
Add the Customize Application Permission to the Enabled Permission Sets and Save
Permission set has been added to the user.