In order to transport fuel you need to transport it within fuel tanks, usually be creating a dedicated fuel tanker design with a large number of fuel tanks. You will probably also want to check the tanker checkbox in the uper right of the design screen for your tanker design as that gives you access to various fuel loading/unloading orders.
Maintainance supplies can be shipped using engineering spaces but using maintainace storage spaces allows for larger quantities to be shipped. Again tick the supply ship checkbox in the upper right of the design screen to designate it as a supply vessel, giving you access to supply loading/unloading orders.
There is no minimum ammount of storage required in order for a ship to be a tanker or supply ship and you can have a single ship fill both roles. Indeed I frequently have my jump tenders serve as maintainance supply ships/tankers/colliers as you need to bulk them up to their jump limit.
To drop off maintainance supplies at a colony the ship has to first be designated as a supply ship, you will then be able to use the order "unload 90% maint supplies to colony". Simply unchecking the order filtering checkbox does not make the extra orders for moving supplies/fuel around visible.
If you are wantig to transfer more/less than 90% to a colony you will need to do so manually via the miscellaneous tab of the individual ship details screen.
