The dictionary definition defines 'namely' as:
'that is to say'
'specifically'
It is an adverb and we can use it when we make a statement and then we want to be more accurate or more specific about what we just said.
Some groups of people are more vulnerable during the cold seasons, namely the very young and the very old.
Do not forget, there is always a comma after the main sentence and before namely.
Some sports are dangerous and should be banned, namely boxing and wrestling.
Notice that usually the first statement is a full and complete sentence, followed by the comma, and followed by namely and a noun phrase (the noun phrase is not a complete sentence and depends on the first sentence for its meaning).
Complete sentence + , + namely + noun.
The sales of some books included in the graph rose, namely self-help and science-fiction.
'Namely' is a useful word in Task 2 when you want to expand your points and give examples, which is what the marking criteria requires you to do. For example:
The planet is being destroyed as a result of man-made inventions, namely factories and cars.
It is also useful in Task 1 when you want to give examples of data to support your point, which is again what the marking criteria requires you to do.
Some countries saw a slump in numbers of visitors, namely the USA and China.
Synonyms of 'namely' would include 'specifically' or 'more specifically'.
Some countries saw a slump in numbers of visitors, specifically the USA and China.
Some countries saw a slump in numbers of visitors, more specifically the USA and China.
I hope this helps! Give it a try next time you write!