Multi-select custom fields allow you to add more than one custom field to the object you want. In other words, you can assign multiple custom field to a person, project or an invoice.
Multi-select custom fields can only be used as dropdowns.
To add a multi-select custom field, go to Settings > Custom Fields > select the object you want to add it and hit Add new custom field:
From the menu, select Multi-select field:
Be sure to define the name, add a description and add all the options (and add colors to the field):
Hit Create field when you're done.
Now, let's see how to use it in practice: Because the field from the example above can be assigned to people, it can be used in Contacts > People:
To add another field to this object, just click on the edit icon:
Now let's take a look how fill the Filters look:
Notice that they've changed because now a object can have more than one value. For example, using this filter, I'll see people who have Graphic design as one of their skills:
However, if the filter is set to equals ( = ) it will show only the people who fit the exact criteria:
The same applies for multiple custom fields assigned: