do u need the law or its explanation?
every body continues in its state of rest or uniform motion in a straight line unless an unnbalanced external force acts on it
If a body is in a state of rest it will remain in d state of rest and if it is in a state of motion it will remain in a state of motion untill an external force acts on it.


An object continues to be in a state of rest or of uniform motion along a straight line unless acted upon by an external unbalanced force. 
newton's first law of motion :
                     an  object  continues  to  be  in  a  state  of  rest  or  motion  until  an  unbalanced   force  acts  upon  it
it   is  also   called   newton's   first  law  of  motion
pick the one which is very useful to u
uniform motion - also called law of inertia