How do i tell my family this is what i want to do

Hello. Thank you for your question.
If joining the Army is something you really want to do then you need to be straight with your family. Explain the role you are wanting to do and what you'll be doing on a daily basis. If your family are worried about the danger of the job then tell them not to worry. Of course there is always the danger aspect but that's the same in other jobs such as police or the fire service. You may be deployed to countries such as Afghanistan or Iraq but with the mission of 'hearts and minds' rather than a 'war' as such. The danger element is considerably reduced in present day. This is also depends on what role you join, for example I am HR Specialist in the Adjutant General's Corps and my role requires me to work in an office most of the time.
If your family are still not happy with you wanting to join the Army, you could take them to a careers office or a careers event and allow them to ask serving personnel any questions.
The Army offers our personnel so many opportunities ranging from travel to sport to education. It is a fantastic career and will provide you with skills for life.
I hope this helps and I apologise your question wasn't answered sooner.
Zoe