This isn't a silly question mate Just to let you know.
But to answer your question, Firepower allows you to use a Primary weapon in your secondary slot, thus allowing two Primary weapons like having a M395 DMR and a BR85.
The other tactical packages, which is what you're talking about are:
Shield Package
After taking damage, players will notice their shields recharging at a quicker speed than others who have not opted for this package in their loadout.
Mobility Package
Allows unlimited sprint.
Fast-Track
Allows the user to advance quicker in rank.
Grenadier
Increases grenade carrying capacity.
Resupply
Pick up grenades from dead bodies.
Requisition
Allows player to “re-roll” an ordinance drop to see if they want new ordinance choices.
Wheelman
Increases the long term durability of your vehicle as well as how it reacts to EMP charges.
AA Efficiency
Reduced recharge time for armor abilities.
Then there are 'Specialisations', which I will clarify also, in case you're getting confused with them also.
Ammo:
Increased ammo storage
Dexterity:
Speeds up reload and weapon swapping.
Sensor:
Increases both the range and sensitivity of the motion sensor
Awareness:
Ability to see motion sensor even when using scoped-in weapons
Stability:
Steadies your weapon while being struck by incoming fire.
Explosives:
Alters grenade performance, increasing blast radius and decreasing grenade damage received.
Wetworks:
Allows Spartans to Sprint quietly. They also appear as an outline to players using Promethean Vision and perform quicker assassinations.
Gunner:
Increases how long a mounted weapon can fire before overheating as well as movement speed with detached turrets.
Ordnance Priority:
In modes with personal ordnance, offers more frequent ordnance drops to the user.
Hope that helps you.