What is a Modal Verb? English Grammar for Daily Life Conversations

In this video, Alisha answers 5 questions. - Can you explain what is the modal verb? - What does ""get rid of"" mean? - What's the difference between ""supposedly"" and ""supposably"", and can I use them interchangably? - Is it true that we use ""of"" for something that belongs to a ""thing"" or ""animal"" but 's for something that belongs to a human? - What's the difference between If I and If I will? For eg:If I do that and If I will do that. If there's a difference where is that?