Clearing files from history and bookmarks

Hi,
I really hope someone can help with this what I hope is simple problem. I have had my Mac OS X for 3 years. I need to clear files to make more space, however I am unsure what is taking up room as photos and music only account for about 25 gig of space and i have never downloaded any apps or movies etc. I went into Finder, then File, then Find to see if I could find any large files. The History folder was large so I dragged it to the trash, as I also did with many other files, there seemed to be many duplicates of photos and close up face shots that I have no idea how they appeared. After hours of 'deleting'...... they are still all there!!!! This is starting to drive me crazy. I then went into a single folder that had 10 photos, and dragged 5 to the trash and emptied trash, however when I went to view that folder again it said in Finder that there were still 10 photos, however now I can only see 5...... Any ideas what is going on? Do I need to be going into 'Hidden Files"???? I am scared to do something wrong and ruin my computer as I have read that going into hidden files can cause problems. I really need to get more space on my HD. Any help is most appreciated and sorry in advance if my questions are stupid but computers are not my forte.
Thank you