Six going to South Africa will need this (4)
I believe the answer is:
visa
'this' is the definition.
The definition suggests a singular noun which matches the answer.
'six going to south africa' is the wordplay.
'six' becomes 'VI' (Roman numerals).
'going to' means one lot of letters go next to another.
'south africa' becomes 'sa' (abbreviation).
'vi'+'sa'='VISA'
'will need' acts as a link.
Can you help me to learn more?
(Other definitions for visa that I've seen before include "Authorisation to enter a country" , "Stamp affixed to passport as permission to enter country" , "Endorsement allowing bearer to enter country" , "Mark on passport" , "Endorsement made in a passport" .)