Employee Satisfaction Surveys are tools used to measure satisfaction levels of employees in areas such as compensation, performance, policies, processes, team members, supervisors, and engagement levels, among others.
The survey can be designed by HR if the organization is small. There is a lot of information available on the internet on how to design the survey. Alternatively, it can be outsourced to an external party, but their services would be chargeable. They will conduct the survey, analyze the results, and present the final report. In this scenario, the company's HR department plays an important role in defining the requirements for the external consultant.
There is a lot of additional information available on CiteHR itself. I recommend researching this topic on that site.
Hope this information is useful.