Decode

. -> any character. IMO the most used one, eg b..y.le matches bicycle
* -> a character 0 or more times (usually combined with ., eg .*)
? -> a character can occur, but doesn't have to.
[XYZ] -> match any of the characters XYZ in this position
^ -> beginning of line
$ -> end of line

So to combine all of above:
heyy? [dj]ude.* will e.g match: 
"heyy dude aaaa"
"heyy dude bbbbbb"
"hey jude ccccc"
"hey dudedddddd"

And for the usefulness of [XYZ] and ^$:
E.g  you have found 6 words with a given order: winter, summer, autumn, spring, cold, hot
then, you can use
^[winter][summer][autumn][spring][cold][hot]$
which will match any word containing one character from each word in the given order.
For this example, "teapot" matches.