People ask about editing options many times every single day here on YA.
Here are nearly 750,000 answers to it: http://answers.yahoo.com/search/search_result;_ylt=Asf_bspRjouLHyB0zeidJ08jzKIX;_ylv=3?scope=all&category=0&fltr=_en&question_status=all&answer_count=any&date_submitted=all&crumb=f%2FKT.IxMD35&p=editing+programs+or+websites&orderby=rank&add_save_name=Name+your+search&filter_search=true
The very best is Adobe Photoshop CS5, but it is very expensive.
A more sensible choice might be Photoshop Elements (current version is 10) which is Photoshop's smaller cousin - can't do all the same things, but it is much cheaper and perfectly adequate for most people.
Another editing program you can get is the Gimp (free and legal). It isn't pretty, has a big learning curve, but is a great program. http://www.gimp.org/
Or you can go to these free websites, but that option is nowhere near as good as having the program on your computer: http://www.picnik.com (which will be closing in April 2012) or http://www.picture2life.com/ or http://fotoflexer.com/ or http://pixlr.com/ or http://www.sumopaint.com/ or http://aviary.com/
The last three are your best bet for more complicated tasks.
If you are one of the people who have an issue about installing a program, keep in mind that you only have to install it once, yet if you use a website, you have to first upload each and every photo, work it, then download each one again. MUCH more up and downloading in the long run, and when your internet is down, you have nothing. If you only want to edit a few photos, websites are ok, but if you have more, then resident programs are much better.
You will need to do a lot of reading and learning - those skills don't happen without effort. Luckily, there are lots of resources available to help you. Start by reading the program's helpfiles, looking for online tutorials, and checking your library for book