If you start with ammonia, you can pull of an H and replace it with, for example, a methyl group. This is a primary amine.
If you pull off a second H and replace that with an ethyl group, you have a secondary amine. etc.
The amine formed is named N-methylethylamine (although there may be a space in there, I can't think, I'm too sleepy), which means you have a methyl group attached to the N of the ethylamine.