At the bottom of Two Point Hospital lies creating a net of hospitals that will be able to sustain themselves. This means you can't build the entire hospital right away. This will create debt that will negatively impact the hospital's reputation. So, you need to be sensible when building the hospital and make sure it's profitable right away.
The only stable source of income are the treatments the patients receive. Each diagnosis or treatment costs the patient a set amount of money. Most treatments cost more than diagnoses. The prices increase over time, so the illnesses that require more diagnoses are more profitable. Of course, prices for a treatment can be adjusted in the Prices tab. Changing the prices will impact the hospital's reputation.
Unfortunately, you cannot influence the health of your patients. You have to watch out for the most common illnesses and make sure the facilities you build are relevant. Also watch the ques forming for the rooms and make sure they don't get too long. This will increase your profits. Usually, the given hospital has a selection of preferred patients, which is much more extensive and you will have to subordinate the entire hospital to match the needs of those people.
From time to time you will also receive income from other sources. However, they will not be regular. These are rewards for performing a variety of side tasks, such as emergencies. If you complete all the requirements to complete the task, you will receive a predetermined amount of money.
In case of a situation, when you're unable to expand your hospital to the point where it gets you profits, you will have to take a loan. You can choose from three sums - the highest will only become available once the hospital reaches level 5. Consider, however, that if you take the loan, you will have to pay the interest, which is an additional strain on the budget. If you build rooms for the loaned money and nobody comes there, the loan could burry your hospital for good.
The expanses of the hospital are mostly staff salaries. The salaries have to be paid regardless of the financial standing of the hospital. You are, however, able to adjust the salaries at any time. Note, though, that the staff reacts to that and if they're not happy about it, they will simply leave. If you're in debt, you won't be able to hire new people. This will make the budget even worse.
Expanding the hospital also takes money. Each room and object cost a set amount of money. The items usually don't cost much, but the rooms can be a real strain. Especially those more advanced. You can't purchase them initially, or you will drain your budget. The illnesses at the beginning don't require advanced diagnostic equipment. Build these rooms only once the hospital is profitable and patients with more complicated illnesses start appearing.