You will have to select your dwellers and after that you will have the option to apply different equipment to them.
The equipment you can give them will be limited to one per type of equipment they can receive.
Whether it be outfits, backpacks, weapons and even accessories.
They are limited to the levels your dwellers have.
You can't equip a level 10 dweller with a level 17 outfit, as it won't be compatible; but if you could equip him with a level 5 suit, since having level 10, it would be higher than his current level.
The equipment you can give them will be limited to one per type of equipment they can receive.
Whether it be outfits, backpacks, weapons and even accessories.
They are limited to the levels your dwellers have.
You can't equip a level 10 dweller with a level 17 outfit, as it won't be compatible; but if you could equip him with a level 5 suit, since having level 10, it would be higher than his current level.