How do I post a Facebook ad?

On your profile page, go to Ads Manager. There will be an option to create an ad.

That's the simplest way, but you should have a strategy before you do it. Why are you making ads? Who are you trying to reach? What are your advertising goals? If you don't have answers to these, you will just waste your money.

This is a big question. I would recommend checking out Facebook BluePrint (https://www.facebook.com/blueprint) and also the Complete Guide to Facebook Ad Targeting (https://www.advertisemint.com/complete-guide-facebook-ad-targeting/) which is a resource we created to help advertisers get an understanding of their options with Facebook ads.

Can any one help me?

You can do this via both Facebook Ad manager and power editor.

A great resource - I may be bias :-) you can find here a full tutorial - https://www.youtube.com/watch?v=_fhjJN7ALnU