New to Mac / Switcher Tips: Get Info

In the Finder, click on a file and go to File—>Get Info or simply type Command (Apple key) + I.  This will open up the Get Info window, which is full of useful information about your file.  Under General, you will find all the basic information about the file, including its name, its size, its location, the date it was created, and the date it was modified.  You can check the locked box to prevent future tampering with the file. The Name and Extension section is self-explanatory.  The next section, Open With, is extremely useful. If you want to make sure that this file is opened by a particular program every time, then simply choose the appropriate program from the dropdown menu.  For example, in the pic to the right, I have the info panel up for the .MP4 of A Farewell to Arms that I downloaded from the Internet Archive. This would normally open in Quicktime by default.  However, I have changed the settings so that it will be opened by
VLC instead.  All I have to do is click the Change All... button to tell my Mac to open all .MP4 files in VLC from now on.

Additionally, under the Preview pane, I can watch the entire movie if I like.  This is a good way of watching a video file in small while working on other things.  Under Ownership and Permissions, you can change access to certain files, which can be extremely helpful in erasing files that have had their permissions switched beyond your normal control.  Then in the Comments field you can either add your own comments, or sometimes, as with this file,
you will find a link to the location from which you downloaded the file.  Hope this proves useful for you. 
Cheers!