How to add more weapons?

How can I add another weapon in another? What I mean is that as I can add one more weapon in another section of weapon, example: two pistols in its section.

If you're making a wad for ZDoom, the simplest way is to define Weapon.SlotNumber in the weapon actor's properties in DECORATE - then the weapon will be assigned to the slot without removing weapons already in that slot, and you don't even have to redefine the player class this way, unlike with other ZDoom-specific methods for adding weapons.

Obviously I have to put in the name of the section and the weapon?

If you have a custom weapon defined in DECORATE like this:

actor MyWeapon [...] {
  [...]
}

Just add this one line into the definition block:

actor MyWeapon [...] {
  Weapon.SlotNumber 2
  [...]
}

That way, the weapon will be assigned to slot 2. Then, pressing the number key 2 in the game will select this weapon, and pressing the number key 2 again will select the default pistol (or vice versa).

Ahhh okay I understand, which program do you recommend to do it?

SLADE3