Windows users who don't have Internet Explorer 11 - and over 350 million don't - should probably update to that version whenever you can. After January 12, 2016 Microsoft won't be issuing security or other updates for older versions of it's flagship web browser.
Internet Explorer ("IE") versions 10 and prior will still continue to work for most web sites after that time, but they will become more vulnerable and somewhat less functional as time goes on. You can find out which version of IE you currently have here.
Windows XP and Vista users cannot update IE past version 8, so if you still have either of those Windows versions, you should probably install Google Chrome, Mozilla Firefox or another modern alternative as your default web browser, just for some peace of mind.
This would be particularly important of you shop or pay bills online with any frequency.