No matter where you work, as long as you are working for a legitimate business, they will give you some sort of handbook when you start. If they’re smart, they will have you sign that you received it, too. Inside the handbook will give you details about your employment, including sick days and how you can be terminated. Some companies will issue points based upon days that you call off. Others will give you a set number of days that you can be absent prior to them terminating you.
These days will be a total of excused and unexcused days. Some companies are more generous than others.
If it is a genuine illness, they can still terminate you. It all depends on what the illness is and how you’re handling it. If it is the common cold or flu and you’ve got a doctor’s note, it’ll be excused, but if it continues to happen, they can terminate you. You can also be terminated if you have a serious illness but simply called out without discussing it with your employer.
Now, if you have a broken leg or arm, are pregnant, or have an illness that doesn’t allow you to do your job for a limited time, then you can go out on disability. This will require a doctor’s form and an official form to be filed with your company. If you are on disability, your company cannot sack you and you must be given your position when you return from disability.