I'm want to take up birding and don't know where to start.

[cpwm17]

1. Start off with a good bird book

The most popular book now is The Sibley Guide to Birds:
http://www.amazon.com/Sibley-Guide-Birds-Second/dp/030795790X/ref=sr_1_1/182-3482153-3605147?s=books&ie=UTF8&qid=1443740338&sr=1-1&keywords=sibley+guide+to+birds

There are also cheaper versions of the Sibley Guide that just cover the western US or the eastern US if you don't plan to travel too far.

Perhaps this is useful. I haven't used anything like this: https://www.audubon.org/

There are maps in the books for bird ranges, plus here are some sites that should give good places to bird in your area (your profile says Colorado) and the birds you might find in your area:

http://coloradobirdingtrail.com/

http://coloradocountybirding.org/

Plus eBird is a good place to see what's in you area: http://ebird.org/ebird/hotspots

You hear many more birds than you see, so a good knowledge of the vocalizations are very helpful, if you are so motivated.

http://www.amazon.com/Stokes-Field-Guide-Bird-Songs/dp/1607887843/ref=pd_sim_14_2?ie=UTF8&refRID=07Z5QW0PKSD0PS3RTJDE&dpID=51mj4fqK2HL&dpSrc=sims&preST=_AC_UL160_SR144%2C160_

Here is also a site the has bird vocalizations from all over the world:
http://www.xeno-canto.org/

There could be an Audubon chapter in your area that goes on regular bird walks. My father used join them and he enjoyed it.