When you create a helper, it can be accessible from the model/controller/view. Please try to consider making a helper whenever similar code appears several times.
How to make the helper
You can implement the class as you like in the helpers directory, remember to put the charm of T_HELPER_EXPORT. Other than that you can do anything.
class T_HELPER_EXPORT SampleHelper
Add the header and the source file to project files, helpers.pro, then run make.
How to Use the Helper
Use the same as the normal class by including header file. There is no particular difference compared to the way the normal class is used.