The introductory phrase can be a bit confusing, but it’s probably one of the easiest rules to remember.

EXAMPLE:

1. If she goes out to the bar, she will get drunk.
2. “So, that’s what you meant.”
3. When that happens, you run.

All of those have introductory phrases or words.

PRACTICE:

Example:

1. When the world goes round I feel dizzy.

RESOLUTION:  When the word goes round, I feel dizzy.

2. Well that’s just perfect.

RESOLUTION: Well, that’s just perfect.

Concluding words are a bit easier. Tag on a comma just before the concluding phrase.

EXAMPLES:

1. They went to the party, too?
2. How the hell did you do that, then?

I think you can figure those out those without practice examples.