A scrum is usually called when a ball is passed forward or dropped forward ("knocked-on" in rugby parlance) from a player's hands. The put in goes to the non-offending side. There are a few other occasions when you get a scrum-- for example a team can ask for a scrum rather than a kick in the event of a penalty -- but they are relatively unusual. A lineout occurs when the ball goes out-of-bounds -- or (again in rugby talk) "into-touch". The team which gets the throw-in (and the actual location of the throw-in) depends on the circumstances under which the ball went into touch. Your third question is a little vague. A ball can be kicked away towards your opponent end of the field any time a player thinks they might gain some advantage by doing so. There is no rule restricting the right to kick the ball, although the offside law does limit the right of players on the kicker's side to chase or field the kick.
