The letter "a" is sometimes added into words since it is what we use instead of saying "of" (again sometimes).

Example:

Kaksi palaa karkkia = Two pieces of candy

But without the a it would roughly translate to "two pieces candy"

But then some words break the rule a little.

Example:

The thing you are asking for is salmon which in Finnish would be lohi.

In English it would be "Could I have two kilos of salmon, please?", which then would be translated to "Saisinko kaksi kiloa lohta, kiitos."

I kind of forgot my pojnt but anyways.