Simple struct/union/etc syntax question

[Bob Davis]

This is probably a stupid question, but here goes. I've noticed in people's code that sometimes when they declare unions or structs, there is the string 'tag' as part of the name. I've always wondered, what does this mean, and what does it do? I've just never been introduced to this particular syntax. I always just use

typedef struct
{
int a;
char b;
double c;
} structName;

Am I missing something by using this syntax?

Edit: While I'm at it, I've got another stupid question. I know with the old-style forums, you could use [ccode] [/ccode] to format C/C++ code to be readable. Is there any comparable feature with the new forum software?