Multi-selection for filtering by custom fields

[Rsn]

Hello. I read this material:
http://docs.virtuemart.net/tutorials/administration-configuration-vm-2/225-searchable-customfield-usecase.html

If I understood correctly, the site https://extensions.virtuemart.net uses the choice of custom fields (at the top).
This works even if you just add parameter to the url, for example: ?customfields[34]=music
But there for each field you can choose only 1 option.
(select tag)

How to make it possible to show products related to different values of one custom field at the same time?
To be able to select, for example, both Music and Package (in select Product).
How to write parameters in url?

Thank you in advance for all the answers!

[balai]

You need a filtering solution.
Have a look at Custom Filters
https://breakdesigns.net/extensions/custom-filters