Multi-variant products in Magento’s world are called configurable products. Multi-variation is referred to a type of product that has different variants, for example color or size. The process of creating configurable products is as follows:
- Setup configurable product attribute on Magento. To do this login to Magento admin area > Catalog > Attributes > Manage Attributes.
- Add New Attribute. Define it as Global, and set Apply To to Selected Product Types
- Select Simple Product and Configurable Product from the list and set Use to Create Configurable Product to Yes
- Click Save
More information on Magento configurable products can be found in following article.