When you win or loose the first mission it tells you to Play 2 missions how does that work then ?

Do choose one or do you choose one at random ?

You put the missions into play, they become active (story) missions. You do not automatically play them, the campaign log says what type of mission to play next. (Only forced missions are played immediately. And there are only 3 forced missions, all of them from core - one from mission results and two are agenda forced missions.)

The rebels choose the type of mission the campaign log tells to play next from among the active missions of that type.

RRG, page 17, Missions, Story and Side Missions said:

-- The campaign log lists the type of active mission the heroes
can choose during each Mission Phase. For example, if it
says "Story Mission" the heroes must choose an active Story
Mission to resolve. There is often only one active Story Mission
at a time.

thematically, jabba is offering you potential jobs. you as the rebels choose which adventure to go on. 'get the explosives' or ' help with a drug trade.'