Salaries is a payment made to employees of your company, the salaries may be specified in an employment contract. Salaries are typically paid monthly, breaking the total annual payment into 12 equal payments (or part thereof). The Payroll app manages all this for you.
Salary changes are tracked in the Payroll app for each individual, providing a total record of all payments to all individuals working in the company and drawing salaries.
See the video below for an overview of the salary capabilities in the Payroll app: