A quick Introduction to attributes
Attributes in Mail Designer Campaigns are basically advanced tags on contacts, that allow you to filter your subscribers based on their profiles.
Attributes are completely flexible and you can assign an unlimited amount of attributes and values to a single contact.
Let's look at some examples for easier understanding.
Let's assume you have the following contacts in your subscriber list
As you can see from this list you already have a bunch of information on these contacts based on their interests. How amazing would it be to be able to use this information for targeting your subscribers in your Newsletters? Now let's look into how you would do this in Mail Designer Campaigns.
What are Attributes?
You are probably familiar with Tags. Attributes are basically an advanced version of tags and they work like this. Based on the above list let's say we want to be able to filter the user group by Language. So we would create an attribute called language and attribute values for English, German and French.

Next we could create an attribute for clothing type containing the following example values: T-Shirts, Sweaters, Accessories

You could then add an additional attribute for Gender or Interest groups, etc. You get the idea.
Attributes and values are 100% customisable in Mail Designer 365 Campaigns, so you have full flexibility and you can target your subscribers leveraging all information you have about your users.