First of, a jet is a reaction engine, meaning that it uses combustion to produce thrust.

A jet aircraft uses these jets to go to high speeds at Mach 1, more or less the speed of sound. Fighter jets go even faster, at Mach 1.3 - 2.2.

To reduce drag, engineers streamline the jet's body, usually curvy surfaces. However, some jets have sharp edges in the sides. These are called Chines, a lifting attachment that also reduces turbulent drag.

Most gets follow a backward swept wing to reduce shockwaves caused by air resistance. In some cases though, there will occasionally be forward swept wings (as the Su-47). They do the same, but risk aeroelastic flutter (the annoying swaying of wings you sometimes get).

A jet's body is usually titanium (for fighters) or aluminum (for subsonic jets), both being light. Unlike prop driven aircraft, fabric "envelopes" are too weak to withstand the high speeds caused by jets.

So, how to make a jet in SP vanilla? Build as you would build a prop plane, but instead of a prop in front, it will be a jet at the back. Be sure to use Structural Wings too, or suffer the aeroelastic flutter at high speeds, regardless of sweep.