I downloaded using zip -- not knowing what the other two options were. I find in my download section an smf_1-1-12_instal-1 folder with various subfolders, beginning with Themes and ending with a file labeled agreement.txt. Clicking on the folder merely rearranges the files within it. What should I do now. Am I having trouble because I'm using a mac?
You need to upload the contents to your webserver
you've done step one, now go to step two
http://wiki.simplemachines.org/smf/How_do_I_install_SMF
also this is also a guide
http://wiki.simplemachines.org/smf/Installing
Welcome to SMF.
The links posted above should get you on the right track. Were you able to complete the install?