TLEPropagator class in package
org.orekit.propagation.analytical.tle needs to be used to propagate a TLE. Using any other propagator will yield invalid results, because the TLE needs to be “unpacked” and propagated with the same assumptions with which it was constructed. The SGP4 model is the sum of those assumptions, and it is implemented “under the hood” of the
An example that illustrates how to propagate a TLE is written in Python using Orekit’s Python Wrapper, and is available here. A Java implementation of this example is similar.
I also find the tutorial on Propagation super helpful in understanding the basic concepts of propagation in Orekit. The examples there use a Keplerian Orbit Propagator, but the TLE propagtor can be used instead. The example prints the PV coordinates on the console, having the propagator either in Slave, or Master Mode. Master Mode is recommended for its rich features.
The Frames tutorial is also rich in content and very helpful.
Generally, the reference frame for a TLE is the TEME frame, but in Orekit, you can request the PV coordinates of the propagated state in any convenient frame, frame transformations are elegantly handled under the hood. The Python tutorial in block  illustrates this with the method
pv = propagator.getPVCoordinates(extrapDate, inertialFrame). Just by providing a date and the needed frame of reference (which is instantiated earlier), the coordinates are returned.
Any questions are welcome!