What is the difference between check it and check it out ?Feel free to just provide example sentences.

check it - a command to commence the initial phase of scrutiny. People will say 'check it' before starting a verse on stage.

check it out - out can mean 'location' or 'degree'

location - 'outside'

I'm buying a shirt. I'm checking it out right now.

or

Check this shit out! Check out this shirt over here! Check out how much it snowed outside today!

'extent/degree' - to an extent or degree beyond the initial phase
'check out' - means to examine/scrutinize
http://www.macmillandictionary.com/us/dictionar...
[transitive] to examine someone or something in order to be certain that everything is correct, true, or satisfactory

'out'
[too difficult to explain]
http://www.merriam-webster.com/dictionary/out
a : to the point of depletion, extinction, or exhaustion <the food ran out> <turn the light out> <all tuckered out>
b : to completion or satisfaction <hear me out> <work the problem out>
c : to the full or a great extent or degree <all decked out> <stretched out on the floor>