In modern fencing, the first and probably most commonly used weapon is the foil.
This started out as a practice weapon, also known as the “smallsword”, to teach the defensive part of sword-fighting, in the days when duels were still fought and it was important to learn how to stay alive. These days, of course, fencing is a very safe sport, and the aim is only to gain points, not to injure the opponent!
Hits are made with the point of the weapon only, and the trunk of the body is used as target, to encourage the defence of vital areas when fighting for real. Because of this, even in modern foil fencing, if a hits falls off-target the fight is stopped briefly although the hit doesn’t count. If both fencers hit at the same time, there are rules concerning "right-of-way" which help decide which of the fencers (if any) gets the point. This again encourages defensive actions to avoid an incoming attack before attempting a riposte.
It is the weapon on which most beginners start, because even if they eventually move to another weapon, foil fencing contains many principles and movements which are also relevant to the other weapons.