Campaign meta fields are used to "categorise" or tag campaigns that are being sent out of the account. An additional step can be added to the sending workflow which allows (can be required) the user to select or input tag for the campaign. Admins users can set it for users to select predetermined options or simply have a free text field.
So set these fields up you will need to use a group admin account, once in the admin view edit a user's settings and search for "Campaign meta fields". From there you can start to set up your fields, like so:
First you will name the type of fields you are setting up, in this example I will be naming the tags "comm type" the aim of this is that users will need to tag the type of comm they are sending out. You also have a option to insert a "note" in the second box which is helper text. As mentioned previously you have the option to choose a free text field, which allows for a user to manually input a tag. As best practice consistency is key so I suggest for the admin set up options through "multiple choice" just so when you are pulling data the fields are consistent.
As you can see in the image I have filled in my options and selected the "allow multiple answers", with this options active users are able to choose more than one option and if this options was unticked (inactive) they would only be able to select one.
In this example I have the option "Required" ticked, this means that selecting/inputting a meta field is mandatory which means the user will not be able to send the campaign without selecting one.
There is also the option to "remove value when campaign is copied", as the name suggests while this is active any campaign you copy that has meta fields attached will not be carried over.