Transposons replicate via an RNA intermediate... Please explain.

Transposons are defined as jumping genetic elements that can jump to different locations within a genome. 

Transposons that replicate via  RNA intermediate are called retrotransposon. Retrotransposons  are the types of transposon that copy themselves to RNA and then back to DNA  so that that may integrate back to the genome.

Reterotranspososn copy themselves in two stages

1)  from DNA to RNA by transcription,

2)  from RNA  to DNA  by reverse transcription

The step in which RNA is formed back from DNA is carried out by a reverse transcriptase which the retrotransposon encodes. The DNA copy formed can be added to new location within a genome.

Reterotransposons behave very similarly to reteroviruses.