The Prime Directive

In the universe of Star Trek, the Prime Directive, Starfleet's General Order #1, is the most prominent guiding principle of the United Federation of Planets. The Prime Directive dictates that there can be no interference with the internal development of alien civilizations, consistent with the historical real world concept of Westphalian sovereignty.
It has special implications, however, for civilizations that have not yet developed the technology for interstellar spaceflight ("pre-warp"), since no primitive culture can be given or exposed to any information regarding advanced technology or the existence of extraplanetary civilizations, lest this exposure alter the natural development of the civilization. Although this was the only application stated by Captain Kirk in "The Return of the Archons", by the 24th Century, it had been indicated to include purposeful efforts to improve or change in any way the natural course of such a society, even if that change is well-intentioned and kept completely secret. "Pre-warp" is defined as any culture which has not yet attained warp drive technology and is thus, implicitly, unaware of the existence of alien races. Starfleet allows scientific missions to investigate and secretly move amongst pre-warp civilizations as long as no advanced technology is left behind, and there is no interference with events or no revelation of their identity. This can usually be accomplished with hidden observation posts, but Federation personnel may disguise themselves as local sentient life and interact with them.
The Prime Directive is a Starfleet regulation, and thus only applies to Starfleet officers. Civilian citizens of the Federation are not bound by it. In fact, if a Federation citizen has chosen to personally interfere with another civilization, Starfleet is powerless to remove that individual, under penalty of court-martial.^[1]
The only stated exception to the Prime Directive is the Omega Directive, in which a captain is authorized to take any means to destroy Omega Molecules when detected. Whenever the Omega Directive is in force, the Prime Directive is effectively rescinded.

Hyperdrive technology is different from warp technology.  The Millenium Falcon, Han Solo's modified frieghter has a modified hyperdrive that goes .5 past light speed.  Star Destroyers go at light speed.  Most Rebel ships go at hyperspace (past light speed), while most Imperial ships go at light speed (except the Tie-Defender).