When people come to Malta, they hear the word Mela a lot, and often don't know what it means only to start using it based on their assumptions hours later.
Simply put, Mela is a universal Swiss army knife equivalent of a word. It can go anywhere, and mean anything, all depends on the context it's used in. The most common usage is for starting sentences as a replacement to the word "so" or alike. For example: "Mela, take bus 44 to Valletta and get off at Floriani"
Other uses of Mela include punctuation. In this case the word is simply inserted instead of a comma and a optional pause is used. It is also worth nothing that native Maltese speakers often use the word as a replacement for a term they do not know the right word for as long as the other party in the conversation is able to understand what was meant.
I have witnessed a telephone conversation where six out of the eight words exchanged by one of the parties was Mela. Another example which you might see: a local enters a restaurant and exchanges the Mela greeting, then asks for a table using the same word and the waiter points to the table and replies with the known word. The thank you is the same word again. That's five times in 30 seconds.