Q: Newby to Mac

Hi, I am a total newby to my new Mac.  I have been using a pc for years. 

I really need some helpful resources on how to download and install programs and more importantly, where to find them afterwards.  I am used to picking the folder to download.  Do I have to save everything in the documents folder?  Can I create different folders and sub-folders like on my pc?  how do I do this?.00