Traveller is necessarily a framework, describing the barest of essentials for an infinite universe. A group involved in playing a scenario or a campaign can make their adventures more elaborate, more detailed, more interesting with the input of a great deal of imagination.There's lots to comment upon there, but two things stand out to me. First, Traveller, like D&D, owes its primary inspirations to literary sources. Second, Traveller assumes that what we nowadays call sandbox play is integral to the success of a campaign.
The greatest burden, of course, falls on the referee, who must create entire worlds and societies through which the player-characters will roam. One very interesting source of assistance for this task is the existing science fiction literature. Virtually anything mentioned in a story or an article can be transferred to the Traveller environment. Orbital cities, nuclear war, alien societies, puzzles, enigmas, anything can occur, with imagination being the only limit.
The players themselves have a burden almost equal to that of the referee; they must move, act, travel, in search of their own goals. The typical methods used in life by 20th century Terrans (thrift, dedication, hard-work) do not work in Traveller; instead travellers must boldly plan and execute daring schemes for the acquisition of wealth and power. Again, the modern science fiction tradition provides many ideas and concepts to be imitated.
Above all, the referee and the players work together. Care must be taken that the referee does not simply lay fortune in the path of the players, but the situation is not primarily an adversary relationship. The referee simply administers rules in situations where the players themselves have an incomplete understanding of the universe. The results should reflect a consistent reality.
Congratulations on your entrance into the universe of Traveller!
I mention these points in part because I've begun to realize how much of how I view old school gaming is rooted as much in Traveller as in D&D. Indeed, I suspect, if I were honest about it, I'd probably find that the gaming philosophies implicit in Traveller eclipse those of D&D in terms of their influence on me. D&D may have been my "first love," but Traveller was my "true love" and, even though I don't play it anymore, it's hard to deny the permanent effect that masterpiece of game design has had on me.