humm you say it like ter-veh-ttuh-loah. notice the double t when pronouncing. of course all together without h sounds.. if you get what i mean. look at the pronounciation lesson
terve means healthy and it's used as a greeting.
tulo means something like a 'coming' and the suffix -a is the partitive.. so tuloa means something like 'of a coming'.
i think you got confused by that doubling of the t. well you see, when you have a compound and the first word ends with a vowel and the second starts with t, the t is doubled. but you never write it as doubled.
tervetuloa=tervettuloa.