I read SO nearly everyday and mostly there is a thread about source control. I have a few questions. I am going to use SVN as example.

1) There is a team (small, large dosnt matter). In the morning everyone checks out the code to start working. At noon Person A commits, while person B still works on it. What happens when person B commits? how will person B know that there is an updated file?

2) I am assuming the answer to the first question is "run an update command which tells you", ok so person B finds out that the file they have been working on all morning in changed. When they see the udpated file, it seems like person A has REWRITTEN the file for better performance. What does person B do? Seems like there whole day was a waste of time. Or if they commit their version then its a waste of person A's time?

3) What are branches?

thanks, and if anyone knows a laymen terms pdf or something that explains it that would be awesome.