Putting student union or student society roles on your CV is an effective way of demonstrating portable skills, like organisation and project management. Therefore, it's a good idea to mention such extracurricular responsibilities if you don't have much formal work experience.
To put student union or student society experience on your CV, you should:
note the role in your education section
write a separate work history entry with more detail
Here's how a society role might look on your CV:
[rg_component id=" 20091"]
And here's how you should enter your student union experience in your work history section:
[rg_component id="20092"]