URDF or Xacro?

I am new to ROS and I have been using SolidWorks Exporter for generating URDF for my robot. Things didn't go well adding transmissions and controller plugins, Gazebo crashes if I spawn the urdf with controller plugins and transmissions, so I started studying other robots in ROS in detail (for example universal-robot) and all of them had Xacro files. Should I also use Xacro? Or the URDF generated by SolidWorks should work fine with transmissions and controller plugins? If I should use xacro, how do I generate a Xacro? Thanks for your attention.