Depending on the X-Cart edition, your store may already have the add-on Shop by Brand installed and enabled.
If not, it can be obtained from X-Cart App Store. To install the add-on, follow the steps described in Installing Add-ons from X-Cart App Store.
Brands are based on the product attributes feature, so you will first have to deal with attributes to configure brands.
Namely, you will need to create a global attribute field that you will use for brands or choose an already existing one - like "Brand" or "Manufacturer."
To create/edit global attributes, on the Classes & Attributes page, click Edit attributes opposite the Global attributes item.
This opens a list of your store's global attributes.
In our store, we have an only global attribute on this list - "Manufacturer":
If we want we can use this attribute for brands. Otherwise, we will need to add a new global attribute using the New attribute button:
This new global attribute can use any name we require.
Once you have a global attribute for brands, you need to tell the "Shop by Brand" add-on that you will use it for brands. This can be done using the setting "Which global attribute field is the product brand?" on the Shop by Brand add-on settings page.
To access the add-on settings page, find the add-on Shop by Brand on the list of your store’s installed add-ons (My Apps section) in the Admin area and click on the link to configure the add-on settings (can be found next to the add-on name and description).
Detailed information on the "Shop by Brand" add-on settings is available in the section Shop by Brand Add-on Settings.