Step 1: Download SQLPlus from Oracle:

http://www.oracle.com/technetwork/topics/linuxx86-64soft-092277.html

Step 2: Install it using RPM

su -
rpm -i oracle-instantclient12.2-basic-12.2.0.1.0-1.x86_64.rpm
rpm -i oracle-instantclient12.2-sqlplus-12.2.0.1.0-1.x86_64.rpm

Step 3: Then, use it

LD_LIBRARY_PATH=/usr/lib/oracle/12.2/client64/lib /usr/bin/sqlplus64 
#e.g. to connect to a remote database
LD_LIBRARY_PATH=/usr/lib/oracle/12.2/client64/lib /usr/bin/sqlplus64 system/XXXX@host:port/SID

# For simpler handling, create an alias:
alias sqlplus="LD_LIBRARY_PATH=/usr/lib/oracle/12.2/client64/lib /usr/bin/sqlplus64"

Step 4: Do some formatting

Once inside, you have to do some formatting, otherwise SELECT statements are quite ugly formatted:

Set Serveroutput On
SET LINESIZE 512;
SET WRAP OFF

The SET commands are documented here:

https://docs.oracle.com/cd/E11882_01/server.112/e16604/ch_twelve040.htm#sthref1904

Step 5: Use arrow keys for history navigation

There is tool which can do this, it is called rlwrap (see here). Short summary to install it:

sudo yum install rlwrap
# and then, adapt your sqlplus alias:
alias sqlplus="LD_LIBRARY_PATH=/usr/lib/oracle/12.2/client64/lib rlwrap /usr/bin/sqlplus64"