In the plugin download section you can download the variables and color palette.
Download variables
You can choose whether the HTML: font-size is 62.5% or 100%. This is important because the pixels will be converted to REM according to this option.
I recommend using 62.5% which is the default setting in Bricks builder, if you decide to use 100% remember to change the setting in Bricks builder.
Variable category
Bricks builder can organize the variables in categories, Figma variables will take the first level folder as category.
For example, if colors are organized in folders, but have a parent folder called Color Palette, in Bricks all colors will be inside Color Palette.
Download color palette
Simply download, it will download all color type variables from figma.