On a Mac, can I move my dock bar to the left hand side?
Also, if I want to have my downloads folder on my screen (not on the dock, on my 'desktop'), is that possible?
Yes to both.
Open the dock preferences by right-clicking on the dashed line crossing the dock and clicking Dock Preferences. There are 3 buttons in the preference panel to select the dock's position: Left, Bottom, and Right.
To put the Downloads folder on your desktop, open the Finder, right-click on the Downloads folder and select Make Alias. A new folder symbol with arrow on it, probably called Downloads Alias, will appear in the Finder. Just drag that to your desktop. Rename it to anything you like. The real downloads folder will remain where it always was, so your programs will still know where to find it. But now you can open it by clicking the alias you dragged to your desktop.