I'm fairly new to Mound and Blade Warband, but I have watched youtubers play and they always have an option to give their soldiers (Just normal ones) the rest of the loot and equip them after the end of a battle When i win a battle i can only equip weapons for myself and the rest is sold i can only guess? Is it a mod i need to download or what?
It is not possible in the default Mount and Blade: Warband. There are several mods which provide such functionality, though i think most mods, for example Floris, only have automatic distribution of loot to your heroes, not your troops.
I can't think of any mod that allows full customization of troops but since there are quite a lot of mods, you might find what you are looking for in the Mod list
You are able to customise the equipment of your heroes, either by talking to them individually through the party screen or in some mods, like Floris, you also have the option of auto-updating it from a communal equipment pool.
As far as I know, none of the mods allow you to customise the equipment of your regular troops, although you can do this through Morgh's Editor, as has been mentioned in a post above.
You can also create your own Knighthood Order in Prophecy of Pendor, and you have the ability to customise the troops that are produced, both in terms of equipment and training.
If you feel that the troops in Warband are a little limited, then you can also use a mod like Floris to expands upon the troop trees of all factions. That might give you more of the experience you are looking for!
Here is the way to change nearly Everything on warband.
I Think all moders are using it.