1. Links two grammatically complete clauses, but marks a step forward, from introduction to main theme, from cause to effect, or from premiss to conclusion, e.g.

To commit sin is to break God's law: sin, in fact, is lawlessness.

[or an em-dash may be used:
To commit sin is to break God's law — sin, in fact, is lawlessness.]

2. Introduces a list of items (a dash should not be added), e.g.

The following were present: J. Smith, J. Brown, P. Thompson, M. Jones.

It is used after such expressions as for example,

namely:
the following:
to resume:
to sum up: