I'd like to add a small note on usage. This 'should' construction today seems formal, and also rather literary. Don't just use it instead of if in everyday English.
"Should" is used in conjunction with "if" to express a possible future state that is considered somewhat unlikely to occur. This is in contrast with "were to", which suggests a future state which is considered highly unlikely or impossible. For example:
If he should come today, I would greet him heartily. -or- Should he come today, I would greet him heartily.