Oracle API Manager is installed alongside Oracle Service Bus. The first step is to install WebLogic: the steps that WBCV followed to install WebLogic are described in previous steps. Once WebLogic is installed, the Oracle Service Bus needs to be installed.
Details on how to install WebLogic are here:
In order to install Oracle Service Bus, log into a Unix shell console as the Oracle user and change directory to the location where the installation binaries are located. Then, follow the instructions here to start the Oracle installer program:
PATH=<JAVA_HOME>/bin:$PATH export PATH java -jar fmw_18.104.22.168.0_osb.jar -log=$HOME/logs/OSB_install.log ...