Hello,
Unless You are recovering a router from bad internal CF and it either (a) has no HDD or (b) previously You did not make a single snapshot from CF to HDD, then You should use jinstall-* package.
install-media is a binary image which one needs to copy to USB stick/CF/PCMCIA card, instuctions are supplied in accompanied Readme file, I believe.
Then one has to slide USB stick/PCMCIA card into corresponding slot on RE front panel and then power-cycle the RE.
Once power-cycled, assuming RE has intact internal CF, then RE will proceed to boot from USB/PCMCIA, unpack and install JUNOS into internal CF.
HTH
Regards
Alex