Find the boot menu
there is some missing features depending on devices firmwares
the site/forum/wiki is well documented-read it thoroughly
Be aware that things can go wrong do a full backup of your system.Your guaranty will be voided.
The easiest way to install is from an external SD card with the Zip.file corresponding to your device.Do folow the wiki instructions & verify the Checksum signatures !
Default Replicant wallpaper
All the goodies:default apps &much more from F-Droid repositary
Catlog a very usefull app to visualize system running & issues
You shouldn't assume that Replicant makes your device 100% free, because it does not. Devices running Replicant all still run proprietary software, to a different extent. Some still have proprietary bootloaders, some don't (e.g. GTA04) but all of them have chips that run preinstalled proprietary firmwares and a proprietary modem operating system. As a side note, to be complete on that topic, on Samsung devices, the modem firmware (non-free) is actually loaded by Replicant onto the modem (it is not distributed with the system but is rather preinstalled on the phone).