When it comes to machinery and construction vehicles the law varies on what you do and dint need a license for and also depends in where you are working. Often the laws regarding licenses are different when the vehicle is being used on private land or a private worksite to if it is being driven on public roads or used on a public site.
It if it often down to the employer to ensure that anyone using a machine or vehicle is competent to do so. They need to have been given the adequate training and now how to operate it safely. Often this is enough to allow them to use it. If they do require a special license to drive a machine then the employer may cover the costs to put the employee through the course or they may cover part of the cost. Other times employers will only ever employ people who already have their licenses.
Insurance is another important factor to consider when it comes to diriving construction vehicles. Often the employer will arrange the insurance but if you are self employed you may have to provide this yourself which can be quite costly.