These are missions you're allowed to take from the beginning of the game, with no prerequisites besides the capabilities of your ship. They're typically made available in the Mission BBS.
Passenger Ferry[]
There are passenger ferry missions that typically pay 5k credits each. A pittance, but they hardly take up any cargo capacity. There are unique variants for the Wild Geese, Rebels, Polaris and Aurorans.
Cargo Delivery[]
There are cargo delivery missions that pay 15k credits each, but will fill up a Shuttles cargo hold completely.
Rush Delivery[]
This is a cargo delivery with a due date. Pays double at 30k, but also requires double the cargo capacity. You have a month to complete it.
Urgent Delivery[]
This cargo delivery pays 60k, but requires quadruple the cargo capacity and must be completed in two weeks.
Passed Delivery[]
This is a cargo delivery that has been passed off to you by a person ship in flight as they weren't willing to divert to the destination planet. It pays 75k.