Playing with Photoshop

So far I have done little or nothing as far as any editing or enhancing, other than adjusting some levels. Just got Photoshop this week and started to play around with it, so I picked some of the pictures I have already posted here so you can see the difference.
Links to the original posts are above each picture

 http://picsandsoundbypeter.blogspot.com/2010/07/grace-and-caleb.html

http://picsandsoundbypeter.blogspot.com/2010/11/frosty-morning-sunrise.html

http://picsandsoundbypeter.blogspot.com/p/people.html

http://picsandsoundbypeter.blogspot.com/p/birds_31.html