How do you branch and merge with TortoiseSVN?

You can also try Version Control for the Standalone Programmer - Part 1 or perhaps Merging with TortoiseSVN.

Version Control with Subversion

A very good resource for source control in general. Not really TortoiseSVN specific, though.

My easy click-by-click instructions (specific to TortoiseSVN) are in Stack Overflow question What is the simplest way to do branching and merging using TortoiseSVN?.