A business plan serves to show the justification of undertaking a business venture. Regardless of the impression that an idea for a business venture is excellent, it is only through the development of a business and financial plan that it is possible to see how the business realization of the idea could work in reality. In order to make a business decision to enter a business venture, it is necessary to first understand the external and internal factors that are important for the functioning and development of the business. We can influence the internal factors of our own business entity and the external ones very difficultly or not at all. When estimating external and internal factors, errors in the estimation of market size, costs, revenues, required working capital and others are possible. To avoid this in the early stages of starting a business, it is very important to create a quality business and financial plan. This final paper will present an analysis of the business and financial plan in the process of establishing a selected new business entity "LETA" with the primary activity of the business consulting and marketing agency. The selected business entity is established with the aim of performing the economic activity of business consulting for micro, small and medium business entities in rural areas. The main tasks of advising client companies are: improving business and strengthening the market position, marketing and market communication in the placement of goods and services. This paper describes the importance and function of the business and financial plan in founding a company as a fundamental basis for understanding and leading the process of realization of a business idea. The main goal of the paper was to explain the key elements of the business and financial plan and to draw a conclusion on the justification of the establishment of the selected business entity. Only adequate harmonization of the function of the business and financial plan can justify the decision to open an agency and rationally assess the desired course of business.